I just got the 8 Herbie's tube dampers the other day. I put 4 on the signal tubes in my CD7 and 4 on the signal tubes in my Ref 5se. I put them all on at he same time. So far I do hear a difference between the Herbie's and the ARC ones. The soundstage seems a bit bigger and more well defined, a bit more detailed. The bass also seems crisper. But I just got them the other day. So I have not had a chance to spend a lot of time listening with them in the system yet.
CD mats definitely work without a problem in the CD7. I have not tried the Herbie's mat. I have an old Marigo Labs Signature mat that I have had for a number of years. The Herbie's mat is cheap enough, I may order one when I order more tube dampers.
The biggest improvement I have made in my system. Audio Research Ref 5se, Ref CD7 and Ref 110. Was replacing my Furman power conditioner with a Shunyata Triton and Alpha HC power cable I bought here on Audiogon. It was like someone took a blanket off the speakers. The sound did not change, but it was richer, more focused. The Triton seems to emphasize all the best attributes of the Ref 5se. It was just amazing. Every time I make a change I don't see how my system could get any better. To be honest it is getting hard to compare anything anymore. I end up just getting lost in the music,