Quandary

The Benchmark AHB2 and PASS sounds very different. If your speaker is little bright then the PASS could be better, though I would use a CODA or the KRELL DUO XD over PASS on a slightly bright speaker. I find PASS too warm for my tastes.

I have a slightly warm headphone heading my way soon, the RAAL 1995 Immanis. I have the Schitt Aegir Class A amp, which is similar to the PASS, as my amp for these phones with my tuners. It will not be a great match (just OK), The AHB2 would have been perfect because it can blend into that warmth, unfortunately, I recently sold the AHB2.

BTW - Even though the AHB2 was underpowered for my Yamaha NS5000 speakers with some music. I was able to determine what speaker wires worked the best with my Yamaha NS5000, ONLY with the AHB2. The AHB2 is so revealing that I could hear what each piece of my system was adding positively or negatively. I ended up with the Audience FrontRow speaker cables because those had 0 fatigue or anomalies that I could hear via the AHB2. I now use a CODA #16 amp (and FrontRow) with the NS5000 since it is a better power match. The AHB2 is a great amp.

There are some improper 100% Class A amps that run cool, KRELL DUO XD and the Westminster Labs amps. I owned the KRELL and never heard the Westminster Labs. 

I would rotate the Benchmark AHB2, and my CODA #16 for my 2-channel speakers and every time would say that what I was using was currently using was the best combo. I decided that the power and sweetness of the CODA is what I wanted over the super clarity of the AHB2. I also needed to raise cash, so I sold the AHB2. I wish I still had an AHB2 for my headphones which I used with a very warm Schitt Mjolnir v3 preamp.

My 2-channel preamps were very neutral so it can get tricky pairing the AHB2 with them.