Too bright relative to which amps ?

See: https://www.discogs.com/Schubert-Don-Jackson-3-London-Symphony-Orchestra-Schubert-Classics/release/3165380

You don't invalid the warranty by opening the case to change the jumper. You can verify that by asking Audio Gd.

The 'hdmi' input of dac19 is not intended to accept the standard hdmi signal from your computer.

Feeding digital to the NFB-11 is trivially better, as the NFB-11 cannot accept analog input. The RCA cable you mention will not work with NFB-11.

Audio gd SA-1 (four 1704 chips, upgraded firmware) -> Audio gd Master-9 -> AKG K701 (made in Austria, single ended) is nice here. The cable of my K701 has only 3 wires and it is difficult to re-terminate it to xlr, I hope that your version is different.

Equalizer APO is a free of charge, parametric and very good system-wide one.

They have the same dac chip. You are probably implying that all Audio-gd dacs using the es9018 chip sound the same regardless of their implementation. If you have heard a lot of them, fine. Better power supply and better volume control may be more important than more power, which comes as a...

I don't think I can advice how much the price difference will be worth to you. By the way, HD700 is not universally accepted as an upgrade to the HD650.

The NFB29 should be the less bright, and much better, of the two. Don't expect brightness issues with your phones, including the AKG.

Audio Gd updated today an SA-1 dac I have to DSP v7. My first impressions are:   Pros: more clear & precise, less warm. Cons: less romantic sound (less "musical"), more sibilant with bad recordings through Sennheiser HD800.   Pros handily overtake the cons for my tastes, a really...

For loaning the only option is to convince a dealer. If you buy through internet order from within EU, you are entitled to refund (minus shipping expenses) without questions asked if you return it within 14 days.

NOS 11 should be better mainly because of superior power supply (and not so because of the 4, instead of 2, dac chips). For use with NOS 19, you should prefer the C-2 amp to the NFB-1AMP. 

So when the Compass is not plugged to your PC you see no audio device at all ? If yes, you have perhaps disabled the sound card of your PC and you could : plug the Compass, right click on SPDIF Interface, click Show Disabled Devices, Speakers/HP will appear marked disabled, select it, right...

With the Compass 2 as audio device, your headphones & speakers should work when you make the proper selections on the Compass, e.g usb input, H for headphones etc. Of course you must plug your headphones on the Compass. If you want to use your computer's audio devices (e.g use your computer's...