Macbook Pro > (Rein Audio) X-DAC > V200 or O2 > T1 is a sublime sounding set up. Especially via Optical. I've never heard the T1's sound so musical or have so much sub bass. You do lose a fair bit of the soundstage mind, but it's a worthwhile trade off as it basically smoothens out the T1 entirely, adds some additional low end clout, perhaps more forward mids and just a smidgen of extra fun factor.
Out of the V200's they are a touch less detailed, but that additional (additional to Optical and compared to the O2) extra smoothness and sub bass oomph is seriously addictive. Vocals have a bit more weight to them (sometimes too much) but it's very natural sounding.
Then when I want a more neutral or typically T1 detailed and punchy sounding presentation, I just switch from Optical to USB and I get a tiny bit more air and sharpness again. In this sense I'm glad the X-DAC doesn't have asynchronus USB or a kind of USB processing that absolutely mimicks the Optical connection. Here you have a bit of leeway and the option for something a tad more musical or analogue like via Optical and slightly more detailed or neutral via USB.
I did actually contact Jason from Rein Audio to see if I was going crazy or a difference did exist (I did do a heck of a lot of testing and A/B'ing before coming to such a conlcusion mind), and he informed me that USB did indeed sound slightly different to Optical via the X-DAC. He refered to the latter as more "Natural" and "Hi-Fi" like.