Toslink sucks; avoid using it.

The analog RCA outputs are the best to use (you said inputs...I assume you misspoke).

I suggest the Creek OBH-11 Headphone Amplifier, which Audio Advisor has for only $295. It is very good.

If you want to use USB and need a DAC, the Audioengine D1 is only $169 and has USB and optical inputs.

Since the Creek only has one set of input jacks, you might want to get the Cables To Go #28750 Input Switch, which Amazon sells for under $20. It allows you to switch between four analog audio sources and feed the selected source to the Creek.

Just connect the outputs of the switch box to the inputs of the Creek amplifier, and then connect the output of the D1 and any other sources to the inputs of the switch box.

I apologize for only spending $500, but I don't think you will get better sound at any price; those are very good units. 

If you can wait, perhaps the new Oppo HPA-1 will be the thing for you. It's alleged to be out soon, and if it's anywhere near the quality of Oppo's other products, you will be getting a monster for an excellent price. Of course, it's not out yet, so no one really knows, but talk about a deserves brand reputation...

Firefly looks very appealing.  I haven't heard it but S. Mejias in stereophile said "The sweet, detailed, richly textured and colorful sound made for what might have been my very favorite listening experience of the show."

Its digital input is USB, so use that from the Macbook.  If it had Toslink, I'd suggest that too, I don't understand the other poster's comment that it sucks - in my experience it's sonically identical to digital coax (plus it is completely immune to hum or other RFI/EMI problems).

Another choice is the compact but full service NAD D1050, which is a DAC/headphone amp, with 2 digital coax inputs, 2 Toslink inputs, and a USB input, for $500.

Consider Sennheiser HD600 headphones for $400, or NAD Viso HP50 headphones for $300.  Or move up to Audeze LCD-2 for $995.  

I suggest Woo Audio WA6 all tube headphone amp $650 with upgraded tubes $350 -- NOS rectifier tube and 2 6SN7 adapters plus 2 NOS Sylvania 6SN7GTs.  Sennheiser HD600s $400, Analysis Plus interconnects $250, Analysis Plus Pro Power Oval power cords (2) $100 each.  Herbies Tube Dampers (3) $90.  Quicksilver Gold $125 contact enhancer for all connectors and tube pins.  

Geoff Kait

Machina Dynamica