Pass INT-30A with Acoustic Zen Adagio

I have no thoughts on the amp, but I can speak to the speakers. I had them in my system about 6 years ago, and strident or harsh in the high frequencies are the last descriptors I ever thought I would hear in reference to them. I'm glad you are exploring other aspects of your sonic chain to find a solution. 

The ribbon tweeter never induced in me the anguish metal tweeters had in the past, and just like you, I am overly sensitive to those HF nasties. I drove mine with Red Wine Audio 30.2 amp and their Isabellina preamp. Tone, body, warmth, and detailed transparency aplenty.

@jond  I would agree with the high-end vs. budget comment.  However, I've opted to get rid of the Pass and keep the Rogue.  I tried a few different pairs of speakers with the Pass, and it sounded analytical through all of them, including the Adagios.  I have a very strong preference for musical and non-analytical, so it just was not a good match for my ears.  I've been very happy with the Rogue.  It really is an amazing amp for the money.  

@adamaley I wouldn't describe the Adagios as strident at all, it was mainly the Rogue that sounded that way (and it was actually mainly because the amp wasn't fully burned in yet).  What I notice is that with ribbon tweeters, it's like there are ultra-high frequencies being blasted at my ear; frequencies that are most likely truncated with dome tweeters.  This ultra-high frequency noise could be coming through the electrical lines, the amp, etc., but when it's there, it shreds my ears.  I will be staying away from ribbon tweeters from now on, because I've noticed this on three different speakers with ribbon tweeters.

I've had AZ Crescendos for a couple of years now, first with a Pass INT-150 and now since last summer with the INT-60.  Although I haven't used tube amplification in my system with these speakers, I have heard them paired with the (expensive) Triode monoblocks a few times.  My opinion would be that unless you are willing to go up to that level of amp quality you may not improve noticeably on the Pass.