I owned the Pass Labs X350.5 and I was able to try a X350.8 thanks to Reno Hi-Fi. To my ears the 350.8 was dull sounding. The 350.5 had much more excitement. I kept the 350.5. (However later on I did eventually sell it).
Now, I also owned the Cary SL-05 and I thought that it to be very constricted. You would probably be better off getting rid of it.
IMHO that is.
ozzy