I have auditioned dozens of amps and have owned many but in my chain the Pass Labs Xa100.8 has sounded the best to date. There are many great options out there Boulder, Benchmark, Arcam, Anthem and on and on. The 100.8 though I believe is something special, not perfect but for my values in sound reproduction these strike the best balance I have been able to find at any price point. I will list some pros and cons I hope will give a fair overview of them.
Before I start my digital chain is dcs Vivaldi Apex dac with upsampler and clock, holo audio serene preamp (IMO MUCH better than Pass Labs relatively poor preamp options), cardas beyond cabling running in to Kef Meta Blade 1’s in a treated room with meticulous speaker placement. I have owned a variety of speakers with the Pass Labs and have noticed great synergy with all of them, Perlisten S7ts, Revel and Magico.
The one thing I can say with complete confidence is the mid-range with the 100.8 is simply unrivaled by any amp I have ever heard. Nothing even close comes to mind. But would I say these amps are best in every category? No, do not believe there is such a thing but if mid-range is a key aspect for you then you owe it to yourself to audition these. More importantly if you do audition make sure it is in a quality chain and room.
Cons:
They run HOT. I am in Socal and in the summers they make the room miserable. I have AC but not an ultra-quiet one meaning running while trying to enjoy music is suboptimal. Also your power bill will go up! They are hungry! They are heavy. They take about an 1/2 to full hour to hit their stride taken out of standby. With my Perlisten the bass was beautifully controlled, deep, nuanced and detailed. With the blades the bass is a tad loose IMHO. Not sure if 160.8 might help with that. I have heard amps with deeper soundstage but the 100.8 still allows me to very easily visually identify precise placement of depth of each instrument.
Pros
Midrange is phenomenal, voices are extraordinary. I have never heard any amp come anywhere near the body and uncanny realism. I had a neighbor ask about all the live music events I have at home asking if I was in the music business. I can’t tell you how good that made me feel. It is those little moments that help make audiophile insanity seem worth it. With a good chain and proper speaker placement vocalists will be in your room in a way no other amp has come close to reproducing. Other extraordinary reproduction strengths are drums (with exception of bass drum which as mentioned above with blades could be tighter). They are reproduced with uncanny realism, from high-hats to rim taps to the crack if the snare. I listen to ALOT of live music and can say you are getting the drum set represented in your room exactly as if in a live show. Horns, especially the trumpet generally fall short of the mark for me with other amps, the 100.8 with blades give me the depth and detail so many others fall short of. I think it has a lot to do with the treble, what I classify as hi-fi sound vs live event sound. Hi-fi the treble is very airy, detailed and bright where in live events I have never heard the sound delivered that way, it exaggerates the top frequencies throwing off tonal balance, yes you can in the hi-fi lens hear the cymbals as if through a microscope but when it comes to brass instruments that exaggeration overpowers the warm frequencies giving you the bleating trumpet vs the resonate one. The soundstage in my room easily extends 5 or 6 feet beyond the speakers which IMO is more than I really need. Soundstage height has varied with speakers and hard to attribute to an amp but can say width jumps dramatically, compare an ahb2 to the 100.8 and expect nearly double the width.
Conclusion
For pure jazz I have mixed feelings as it will really come down to speaker pairing for the bass end. Cello, piano, trumpet, sax, vocals, all but the very bottom of drums and bass will floor you. However bass drum and bass low end I feel have room for improvement, may just be I need more power with the metas, I can say the Perlisten pairing however was great in this regard but the metas mid and upper range is so much better for now can live without perfect low end. If you are a bass head and want ultra-tight hyper detailed bottom I am not sure the 100.8 would be your darling with inefficient speakers. I would also say I have heard the 100.8 in what I consider subpar chains that really benefit from a top end boost because of lack of detail or dynamics, that airy top end boost helps juice up the deficiencies, put a 100.8 in that chain is a recipe for a fairly boring experience as without a chain with loads of detail the uncanny realism the 100.8 has on tap will never be revealed. I read one post in this thread saying the 100.8 was bright, if its bright in your system you need to either get some decent components in your chain or learn about speaker placement and your room’s effect on sound reproduction, as you have some serious issues as to make the 100.8 bright you are either hearing really bad in room reflections or your chain is ear blindingly bright. If any crticism could be drawn it would be to call the monoblocks warm, but to my ears compared woth live music it is not warm bit spot on. Realism over exaggerated hi-fi.
Just another fools opinion, a dime a dozen. Would however strongly encourage you to give this amp a listen, especially with a dealer who knows their craft and has a demo room that can really show them off. They are truly an amazing feat of engineering. If you follow and trust your ears, you can’t go wrong.