Pass X350.8:
Background on trying this amp was that I wanted to complete the "musical SS" trio of Pass, Rowland, and Luxman. I've always had profound respect for Nelson and in my Zu tenure, tried SIT amps which sounded very, very good. In fact, if I ever go back to Zu a XA25 would be my first amp decision (and Sean Casey's favorite amp right now).
I considered the X and XA.8 series, but thought the latter would overheat my room and at the power I require, be too expensive ($30k+). Also, I've noted several contrarians on the XA.8 series who actually feel the X is better. So I narrowed the Pass decision down to the 260.8 monos and the 350.8. I had read on another forum a member having trouble with the monos on 88db speakers, so I ultimately thought the 350.8 was the best amp to try. YG speakers seem to love power, so why not. I learned later on that the 260.8 is the "jazz" voicing while the 350.8 was the "rock" one - as I listen more to rock that seemed to be the route. Also, for those looking at the XA series - the 100.8 sounds "rock" vs the rest of the series.
I turned the amp on for 5 days, with only a short session at 35 hours that wasn't successful. After 5 days, I really started to examine the amp/speaker relationship. We tried multiple preamps (tube and SS MF) and cables (XLR and RCA). We settled on the LTA tube preamp with single ended cables (it doesn't have balanced outs). Overall the Pass was disappointing and, honestly, didn't get better over the two weeks I had it running in. The amp had a real "stilted" presentation that seemed to slam the leading edge with no decay - to the point it was harsh to my ears. Piano really didn't sound like a piano to me, no matter what I tried. Surprisingly though, the soundstage wasn't overly big either and I always felt the amp exhibited a flatness quality compared with other amps. This was codified in an overall thin timbre where most instruments and vocals lacked body. As one listener here commented, the female voice lacked the vocal chord pipe. I will say the amp isn't cold, was actually warmer than expected, and had a characteristic to the bass I really enjoyed. It hits hard, but with a bit of roundness that I prefer.
One last comment - this amp runs quite warm. Huge heat sinks just emanate heat into the room similarly to Luxman Class A in my experience. It was just on the cusp of being uncomfortable in my 24'x16' room in a hot climate. All-in-all, the Pass X.8 just wasn't synergistic with the YGs and I feel Nelson's best work remains in the lower-powered spectrum.