Well I actually had both amps side by side in my system for a while and the Pass X350.5 is better in every aspect than the FPB400CX.
The X350.5 should be compared to the Krell EVO402 and then they are very close. I had the EVO402 as well and it does sound very similar to the Pass X350.5 but at 1.5 times the price.
For price / performance ratio the Pass is the best.
The FPB700CX is much better than the 400CX and would come close to the Pass X350.5. The 700Cx might even have a little more bass slam.
Peter
The X350.5 should be compared to the Krell EVO402 and then they are very close. I had the EVO402 as well and it does sound very similar to the Pass X350.5 but at 1.5 times the price.
For price / performance ratio the Pass is the best.
The FPB700CX is much better than the 400CX and would come close to the Pass X350.5. The 700Cx might even have a little more bass slam.
Peter