I hate to resurrect such an old thread, but I have an S7i and have recently compared it to two of the best of today's DACs, the Ayre QX-5 Twenty and the PS Audio DirectStream with Huron software.
Of course both can play 24/192 and DSD, which the S7i obviously cannot.
But when it comes to Redbook CD and PCM sources, the Wadia still beats either.
Both of the newer pieces are brighter, to the point of being shrill on some recordings, but the big area in which the Wadia excels is space, or the presentation of it.
Sure guitars and such sound great on the two newer DACs, but through the Wadia they are presented with a palpable sense of space around each instrument, where there isn't just the sound of a guitar string, but rather the sense of a guitar string being played in a space.
I don't know if I'd advise anyone who didn't already own one to pick one up used, but I was ready to upgrade, and I think the Wadia's beauty has just sucked me back in.