Best Bang for $2000 System Upgrade?

Well, it is time once again to go to the help desk of the audiophile world, you guys, for some real world advice on how to "best" upgrade my system staying within my $2000 budget, in the digital domain. I am a drummer who listens to well recorded rock, blues, jazz and vocalists of both genders.

Ok first things first, my gear;
Dynaudio Contour S3.4 spkrs
McCormack DNA-225 modified amp powering Dyns.
Adcom GFA 2535 (90wpc x 4) powering center and rears
Integra DHC 9.9 pre/pro
Source: 1TB external hard drive playing lossless files.

Signal path; Ext HD connected via usb to laptop, usb out to M-Transit USB device, toslink out of transit usb into Integra where d/a conversion happens. Just how bad is this signal combined with the Integra's DAC? Who knows!

Anyway, here is my current thought process, in two stages. The first, for an el cheapo improvement, but an improvement nonetheless, is this;
1. Source; My existing 1TB external drive, backed up by a second 1TB drive for additional cost of $100.
2. Squeezebox Duet, modified by Bolder to be my budget high-end DAC substitute, for $650 (From all I have heard and read, it seems that one needs to spend a minimum of $2500 retail on a DAC to experience sonic performance above that of a Bolder-modded Duet)
3. High quality 250wpc integrated amplifier with home theatre bypass (such as the Musical Fidelity A1008) that sports a better analogue stage than my Integra DHC 9.9). I can get one pre-owned for $2500. This would replace my McCormack DNA-225 for which I could get about $2000, so net additional cost here; $500
4. Integra DHC 9.9 - kept purely for my home theatre needs

Total cost: $1250

BUT......if I wanted to spend another $750 - $1000 using ALL the funds in my budget...How do I get the best bang? Keeping all other things equal, do I;
a) Scrap the external drive as my source and get a quiet, low-jitter 2TB tower built? ($750)
b) Scrap the Squeezebox idea and get a serious DAC? (like the Ayre QB-9 @ $2500) But that adds $1850 putting me over budget. Amazing DAC though...
c) Keep the McCormack, ditch the integrated amp idea (which gives me an additional $500 to play with), and find a nice used preamp or preamp/DAC with HT bypass and superior analogue stage at around the $1250- $1500 mark? Thinking Bel Canto DAC3 or something in that league...

Any and all ideas would be welcome! I do want to spend the extra dough so help me out here fellas! Thanks!
You've got some great pieces. If it were me, I'd look into a quality two-channel preamp and a nice DAC. You'll find a lot of recommendations for both here on the site but personally I think a tube preamp with a HT pass thru would work nicely with your McCormack amp.

What worked for me.

1)Duet (used $250)
2)Bolder digital mod ($325)
3) Parts express power supply ($15)
4)Bolder mod on PS ($100)
5)April Music Stello DP-200 Pre/amp/DAC (used $1000)

All fed thru Bryston HT amp. The dp200 has ht bypass so I kept Yam AVR for HT and now a real nice 2 CH and HT..for cheap.

It hooked me so much on 2 channel I am planning on a huge($$$$) upgrade path for the be careful.
I forgot to second Schipo's recommendation for room treatments. It is truly amazing what room treatments will do to the performance of a system. A good room treatment can give the effect of upgrading every element of your system.
SCP - that is EXACTLY the kind of thing I was thinking about. Except I am not sure what the rest of your system looks like, to make a fair interpretation of your results as relevant to what mine might be (i.e. speakers, and source in particular). And for 2 channel, it is your Bryston that is powering things, correct?

Robert Brown, I am seriously considering the Plinius 8150 and even the beefier, better 9200...

Ethos, I will check that out!

Thanks everyone so far
What I have is a 1TB netgear NAS streaming to the Duet reciever feeding a digital signal thru a Sweetcome dig cable to the dac within the April Music pre/amp that is fed thru Blue jeans cable I/C to the Bryston 5 channel 120 wpc amp. My speakers are Von Schweikert VR4-jr. Music tatstes run from Blues/classic roc/female vocals and a new love for classical.

I had all but lost interest in my music til now. With easy access and the more realistic sound field, I am hooked again.

BTW for Ht I use a Yam RXV863 as the pre/pro fed thru the Bryston to a VSA center and frts and Def tech sats rear and a pair od Def Tech S/C II subs.