Without buying anything, the best thing you can do is optimize your connection and that is going to mean using the internal DAC on the receiver.

This means connecting and delivering a digital signal to the receiver. For your phone your have three option:
1. USB to the front of the device as this will bypass the phone's DAC.
2. If you an iDevice and have the optional DS-A5 module and you are streaming files that are not above CD quality you could connect via AirPlay. Airplay is limited to CD 16/44.1 quality streaming.
3. If you have an Android or Windows OS phone you may be able to connect via Bluetooth. The receiver does not support Apt X as best I can tell so this might be lossy.

For your computer I would connect via WiFi as the receiver supports DLNA. You will likely need to select "Media Server" as the input on the receiver. I use JRiver and there are quite a few other software services availabel. JRiver has a free 30day trial so it is ideal to see if it works. Roon is great software but MUCH more expensive.

The other option is to get an external DAC or Network Streamer and connect to the RCA inputs on the device. How much better an external DAC will sound is debatable. My experience is that the onboard DAC for receivers are better than you would expect though I have only had Marantz and Denon receivers over past 10 years. It has been a long time since I listened to or owned an Onkyo.

If you were to get one, I would absolutely get a unit that has a 30 or 60 day return policy and then test whether you like it better than the Onkyo's onboard DAC. You could be bumping up against the limitations of the amplification circuits in the receiver.

At $649, I really like the Marantz NA 6005 as it has an awesome feature set. The Oppo Sonica at $799 is outstanding. You could try the Cambridge Audio DAC Magic Plus for $345 as it has limited features but I still think it will outperform the onboard Onkyo. I doubt the DAC Magic 100 will.

Also, what kind of BluRay player do you have? That might be a solution via it's onboard DAC or buying something like an Oppo UDP 205 for $1299 or even the UDP 203 for $559 might be a step forward. You would run an HDMI to the receiver and separate analog audio in and it support DLNA and a variety of other solutions for connectivity.

[quote=kcahmadi]Current set up: Klipsch RF-52 II towers, Klipsch RC-62 II center, BIC Acoustech PL-200 sub, Onkyo TX NR737 receiver

Hey y'all so I exclusively play music off my phone and laptop (mostly FLAC) through my receiver. And I was wondering what other audio equipment I can add to my setup to maximize the audio quality coming from my phone/laptop. Would it be an external DAC, a preamp, an additional amp...?

For my money, the speakers you are using are not capable of producing high quality sound.

There are many many speakers from Focal, PSB, Wharfedale, B & K, Vandersteen, and many others that can produce excellent sound quality.

You might look at the speakers that are reviewed favorably in Stereophile. You will notice that yours aren't there, and for good reason. They don't review speakers that they already know are inferior.

Before you worry about other factors, you need to get better speakers.

You won’t find separates that outperform a receiver or integrated amp without spending a LOT more. That is not a wise investment in my opinion.

Klipsch is an unpopular choice in mainstream audiophile circles. That line of speakers is deemed “bright.” I am not sure how familiar you are with audiophile terms but bright is going to mean it has tinny high pitches which is fatiguing for many. I have heard that after about 500 hours of burn in the brightness softens on those a bit but I have no personal experience. Brightness is generally deemed undesirable though there are a lot of bright speakers sold and many people don’t mind or enve like them.

There are two ways to correct brights. One is an equalizer and I found engaging room correction (a very elaborate EQ) on my old Onkyo had a surprising impact on the cheap Polk speakers I was running at the time. It really softened the brightness. The other is to get a very warm amp.

You could add an integrated amp with home theater pass through which would have it function as your front 2 channel amp. This may or may not have an impact depending on the amp chosen. In your given price range, improvements are going to be more a matter of taste.

For instance, you could add an NAD integrated which potentially could have a superior DAC and superior amplification for Music. This could be a huge improvement or if it is bypassing your room correction, it might be an enormous step backward.

Do you have room correction enabled? What is it you like about the sound now and what do you want more of?

So, “bright” speakers tend to have accentuated higher frequencies. This is why they are bright, but also why you hear all that detail. A lot of the more subtle, refined sounds are at higher frequencies.

This can produce some true, Wow moments, but can also be fatiguing through time. If you like that, when you consider a speaker upgrade, Paradigm and B&W are going to be brands you will like a lot.

Boomy bass is driven by your ported subwoofer. They are wonderful for home theater. They deliver extremely low frequencies with modest power and in those rumbling, earthquake type moments it sounds awesome.

For thunder, jet engines, explosions or earthquakes, refinement is not really necessary. Thus a port deliver much bigger bass with a modest amp and minimal refinement.

Sealed subs offer much more refined bass but because they aren’t ported, require a lot more power to deliver the same volume.

If you want, smooth, well balanced bass a better subwoofer will be required. SVS offers a sealed sub with 400w of power for $399. It is available in Black Ash and no other colors. That is the least expensive sealed sub I am aware of on the market. The model is like the SB-12. It will be adequate for a small to medium room. You would need a lot more power for a large room.

Upgrades will deliver better quality and accuracy in sound. A better DAC, a better amp and better speaker will al deliver improvements. In the subs $1K range, a better subwoofer and a better DAC will probably deliver maximum bang for the buck.

That SVS sub along with something like a Marantz NA6005 would be pretty good. That is what I would look at as speaker and amp upgrades will probably be more than $1K.

Best-bang-for-the-buck tweak I've ever tried that actually delivers:
https://www.audiostream.com/content/electrically-isolate-your-networked-audio

Also, echo the comment about using DLNA to stream from your computer, so you'll have to RTFM a bit if you're unfamiliar:
http://www.onkyo.com/manual/txnr737/adv/en/index.html
(Expand the section on DLNA Music Streaming.)