All those things are great but you have to decide if and how you will use them.  They will certainly complicate the setup of a simple 2-channel setup and, considering your imminent aquisitiion of a C21, you need to decide what direction to go in.  Do you want to optimize your 2-channel analog system or do you want to watch TV/movies?  You can do both but you then divide your assets more thinly.

IMO, the HK 3490 is very good, and so is the turntable. Those components can form the core of a good 2.1 system.

I would invest in a decent subwoofer and go with a 2.1 system, which is what I use for both music and viewing with my 60-inch HDTV.

I use a NHT B12D subwoofer, which is excellent, but $700 may be more than you want to spend.

The Klipsch RW-12D is pretty good, and can be had for $350-450.

People say that the FS-51 speakers are quite good for a very low-priced speaker, but you could certainly make a major improvement there by getting some speakers like the Wharfedale Diamond 10.4 or 10.2 speakers...or many others.

I don't know why you want a C-21; that seems to go nowhere. I would forget that.

An OPPO BDP-103 would be an excellent addition, since it is extremely good for playing DVDs, CDs, and SACDs.

endtroducing wrote:

Soon to be moving to a larger space, where there's room for a TV. I'm wondering if it's advisable to add an LCD, receiver, and subwoofer to my current set-up right now, I have Pro-ject Debut III turntable hooked up to Pioneer FS-51 speakers, powered by a Harman Kardon 3490. Any advice? For what it's worth I have a pioneer C-21 soon to be in my hands.

+1 on the Oppo bdp-103.  Sounds great and solves everything. 

always run a speaker wire from either your left or right speaker (using banana plugs) to your subwoofer and use the speaker level input on your subwoofer. if you use the subwoofer out on your receiver the bass might be lagging a lil.

Why do you say that?

Also, using speaker wire from one speaker gets you only half the bass.

that was the way my old stereo salesman taught me. perhaps i was passed on bad information?

I think so.  Mebbe an "old stereo salesman" is not up on proper, modern subwoofer implementations.