I listened to slightly modified SI amp in my system with a SLA driving it. While it sounded really quite good with a lot of promise, I never got around to really dialing it in before I started listening to something else.
As good as the sound was, however, I still craved that shimmering, breathing, warm-but-clear feeling that a good tube pre provides. Since my tube preamp has been out of commission for sometime, however, I never did mate it with the Tripath.
BUT, the ultra-clear sound of the SI reminds me somewhat of the clean and musical presentation of the 47 Labs Gaincard (SI is somewhat warmer but less controlled, though). I used the Gaincard with a Cary SLP-94 12au7 preamp (before the pre pooped out), and it improved the system immesurably. I cannot listen to the Gaincard by itself anymore without feeling that it's just a bit on the clinical side. The tube pre/Gaincard combination was, at times, magical. Bloom and warmth galore, but still with the detail retrieval and quickness of the Gaincard. Nice.
I don't know the technical particulars of the SI, but I can only imagine that a good tube pre might be the ticket to kicking the Tripath amps to the "listen to the music and you won't even worry about the system anymore" level.
Just a feeling, though. I haven't tried it.
Best,
KT