OK I confirmed what Boja said, Dolby headphone isn't available when listening through RCA outs. But he's right in that virtual speaker works fine and produces a very similar result.
@ADD, I measured the the card. It is 170.5mm x 106.8mm x 19mm. The molex power connector adds another 16-18mm to the length when plugged in. So it sounds like it'd be too small for your case anyway.
I spent a little more time listening to the amp section, and it's got about 50+ hours of burn-in now, so I would like to amend my comparison to the Opera a little. The STX's amp is
almost on par with the Opera, but the Opera is slightly better overall. The difference is very small tho. So small that when I use my Outlaw PCA IC's to connect the Opera to the STX, the Opera loses its advantage and I believe they are on equal footing.
However, when I switch to using BJC LC-1 for IC's, then the Opera reveals that it is a slightly better amp. The soundstage is a little more 3D-holographic, and instruments are a little more focused and have slightly more body and presence within the soundstage than they do using the STX's amp. The bass is also a little more present, detailed, and textured as well.
The STX's amp OTOH is a little more forward in the treble region, has slightly more air and a more natural/longer decay to sounds. The soundstage is also a little bit larger on the STX's amp than the Opera, and you're taken a half step back further away from the sound than with the Opera (a point that is neither good nor bad, just different). So with the STX you're standing in front of the conductor's stand, right in front of the orchestra. With the Opera you're sitting in the middle of the orchestra with the Viola's.
However, being the imaging and details freak that I am, I prefer the Opera.
Slightly.