Does your soundcard have surround sound DSPs? Because if so, the difference will be that you'll LOSE that surround sound when using a USB DAC.
If your soundcard does NOT have surround sound, then you may get a marginal improvement in soundstage and positioning with a USB DAC and amp. It won't be as much of an improvement as adding in virtual surround sound though.
I use the same setup with my M-stage. So does Change is Good.
The M-stage is one of the BEST amps I've used for double amping, and it's able to increase the soundstaeg size the most out of all the amps I've double amped with.
So something sounds off with your setup.
My M-stages does the exact opposite. It expands the soundstage size by several feet in all directions compared to plugging in directly into the mixamp.
So again, something seems off. :blink:
Check out the TCC TC-716 6-Way Stereo Source Selector:
http://www.amazon.com/TC-716-Stereo-Selector-BLACK-VERSION/dp/B0001F347K
I have this and I love it.
Just plug all your sources
and all your amps into it, then mix and route them as you please. It's a completely passive device (no electronics inside) so it doesn't affect/degrade the sound. It's just like a box of switchable interconnects.