The closest you're going to get is probably the CJ Premier 350 if you can find one. The CA 200 will get you pretty close as well but again hard to find.. If you want to stay with Pass you're probably better sticking with the older Class A .5 series.
If you can demo the AtmaSphere GaNFET monos, you might find that they hit that middle ground you are looking for. I had a X250.8 and replaced it with an XA30.8 after selling my power hungry Magicos. I found the XA30.8 had more of the ’midrange and very full weighty sound’ compared to the 250.8, but the latter had more treble extension and better bass/dynamics as one would expect. I’m not sure how those two compare to the 350.8.
I recently purchased the AtmaSphere monos and have finally had some time to compare them with the XA30.8 and I actually find they are darker and fuller sounding than the Pass... It’s next to impossible to play something and make them sound harsh! They do give up some treble extension to the XA30.8 (so maybe two steps away from the X series then) but have way better bass than the XA30.8 (and likely my 250.8) with their high damping factor.
If you like the sound of tubes but want some of the benefits of SS, these are definitely worth a listen...
Search for them here:
@marco1 Good tip on 0.5 series. I was reading on WBF that 0.5 series is richer and has more 'soul'. Apparently XS Series combines the detail and clarity of 0.8 but the midrange euphonics of 0.5. But of course XS is pricey.