A local dealer loaned one to me for a demo a few years ago. The sonics were certainly good, but it did not improve on what I had at the time all that much. The build quality was there, but the input selector was noisy and I did not want to go through a possible return to Canada for a replacement. [Classe does offer excellent customer service.] I suppose the dealer could've performed the surgery but my tube-buffered passive was still superior in my system. Note that Classe power amps of this vintage often sell quickly and are obviously still sought after, even though they were made a long time ago, esp. in audio years.
I think the 5 has a "direct" switch and has balanced I/O connections which should be used if possible,
One caveat: The gain is 18 dB, way too high for a CD-based system but many manufacturers are guilty of this also. 20 dB seemed to be the default value in tube preamps, maybe this is a holdover from those days. If you can give it a try in your system, by all means do so.