@dz13 I actually heard the Audio research I50 with the horn $15k+ Avantgarde speakers that were very sensitive. So it definitely was not a bottleneck. I personally loved it, it was nonaggressive and smooth, and it really showcased the strength of the 6550, very pleasant to listen to. Reminded me of the Cayin CS55a with 6550 coke bottle tubes. If you want to relax and enjoy the music, I would say it is worth auditioning.
Having said that, my friend Mr. Kanta did not like it because he said it lacked dynamic contrast but take his observations with a grain of salt because that day we were listening to many $200k+ systems so it is easy to get confused when we had things to compare.