I own the NuForce uDAC (first edition) and the LD Q. I use them both, the uDAC driving the LD Q which in turn drives my AKG K172HD cans, or alternatively my Pioneer A109 MOSFET Class A amp driving a set of KEF 303 Series II matched pair speakers. The Pioneer is set to "direct" so it essentially functions as a simple amp with only volume control, bypassing bass, treble, loudness and balance circuits.
I use the LD Q as an amplifier only. I think the NuForce uDAC a little low on volume produced. The DAC in the LD Q is a total failure. The volume is far too low. It is supposed to get a revision, but as of today I have not seen LD sell/ship the new version with improved DAC. As an amplifier on the other hand it is superb. All in all I am very happy with this setup. The next step will be to replace the Pioneer A109 with a Topping TP60 T-Class (Tripath 2020) amp next month.
The uDAC has MUCH better dynamics, wider soundstage, and better frequency range than any Realtek on-board chipset. I use an ASRock Atom 330 or an EMTEC N200 media streamer as source, both have Realtek chip sets, but better ones than the AC 97 which is one of the worst sound chips ever produced.
Will you hear an improvement with the uDAC / LDQ? YES you certainly will. Better soundstage, sound definition. MUCH better bass. It is a very big improvement well worth the money. You can hear this both with the headphones and with speakers. I think the LD Q is worth the money as an amplifier. It improves on the uDAC's sound.FWIW, my uDAC 1 does not have any hiss/noise, nor does the sound drop out on one side with low volume. The combination uDAC + LD Q produces a superb sound with deep bass, very wide sound stage, brilliant highs and a completely black background.
I would go for a uDAC 2 with LD Mk III and a Class T amp to drive my speakers if I had to buy new now. I would probably go for new speakers with high sesibility (>90 dBA/W/m) as well, so I could go for a low-power T-Amp model
I think uDAC2 -> LD Mk3 -> Topping TP21 -> HLLY MT-3 set or headphones would be a great combination for a small room or desktop setup. The HLLY MT-3 speakers use a great driver from HiVi. Being a single driver speaker (Breitband) they avoid a lot of phase-shifting problems due to cross-over filters, and having high sensibility means you can go for the low-power TP21 T-Class amp and still get enough sound volume. Most of these items can be found cheap on eBay.
If you are not a fan of tube sound, you could skip the LD Mk III. From what I read the Tripath T-Amps already sound like good tube amps.
Edited by MaXMhZ - 12/7/10 at 5:19am