Problems with sound setup, help!!

Hey guys, I would really appreciate some help to diagnose these problems. Here's my setup.

Computer (Auzentech Bravura sound card) -> Fiio D3 -> Schiit Asgard -> HD650.

1- There is a distinct "hiss" coming from the headphones when the amp's volume knob is above half, but this only happens with some sources. It doesn't happen with my phone, for instance, but it does happen with my computer.

2- When I'm connected through my Auzentech Bravura's SPDIF (coax), turning on and off my desk *LAMP* causes a "click" or a "pop" in my headphones. A similar phenomenon happens when I connect the Bravura to my home surround system - but instead of producing noise, the sound stops for a second and comes back when I turn the lamp on or off. This absolutely doesn't happen whatsoever unless I'm hooked to SPDIF. So, I have no clue what kind of interference is happening with the lamp - I tried plugging it on another outlet, another powerbar, on my UPS, etc...

I'm thinking about trying out another sound card, but I'm afraid it might do the same thing? For all I know, it's not the sound card that's the problem - on the other hand, it's been giving me trouble for a while...

What do you guys think? Thanks

I don't usually bump but I'm sure someone here can help me, I've spent quite a bit of money (by my standards) building this little setup, and I still intend to keep working at it, but I need to handle these little problems. I want to grab a Schiit Bifrost but there's no point in doing that if the SPDIF output is faulty.

Nothing particularly long, 6ft coax cable for SPDIF (I tried a 3ft one also, no change), 1.5ft RCA cables between the DAC and amp, and 10ft stock cable for the headphones.

Any other clues? I've been asking and I'm kind of at a loss here.