I have owned both and they are both among the best SS amps out there IMHO. I would say that if you speakers are tube-friendly (high and smooth impedance - e.g. Merlin VSM) I would go with the J if you find any. If you speakers present a more difficult load, the high current of the XA.5s will perform better. Of course, in either case 89db or better sensitivity would be necessary or you might, occassionally feel you have run out of steam - less likely with the XA.5s.
