Amps for Avalon Osiris CAT JL3, Boulder 2060, Dart

"Pos",great stuff in store for you.How about those Amperex's?My best pal's phonostage had them, and superb!!
In response to your question,I have heard the Osiris,and own Ascent Mk -2's.I live in the N.Y. metro area,and have made it my business to become familiar with the vast majority of superb products that are currently available.
The Osiris was/is a SUPER PRODUCT!As you know.You do have to be very careful about cable/component matching to get the most from it.It is an extremely revealing speaker,and is easily competitive with the best of today's stock.
The important thing about amp compatibility is to think "tonal color" as opposed to high volume capability.This can become tricky as there are so many choices,and many people are impressed by dynamics soley,which you will surely get,with the right amp.I have gone through the tube/solid state wars,over my 38 years in this hobby.Love tubes!Hate sitting in my own sweat,in my dedicated audio room,which is a closed off environment!!I guess one cannot have it all.
The finest tube systems(low power)are superb,and have a stunning tonal palette.Solid state,in the past,has not been great here,yet the current crop of "Elite" solid state is closing the door here,Big Time!!!
I have run my superb Ascents(with REL STENTOR sub,coming in at 26 hz)with superb tubed and solid state.I have chosen solid state because the best units are superb,today,and I didn't appreciate sitting in my bathing suit,in December.All while the outside temp was about 25 degrees.
This was a tough choice,but my current highly modded(customized) Rowland,two chassis model 8t,completely fills MY bill.
OK,as to you,and this is only an opinion,the choices are many,yet the way you drive the speaker is important.Will you Bi-amp?Or one amp?I assume you will tri-wire,if only one amp.Room size is important in such a decision.
The Osiris is one of a handful of the "absolute cost no object" best designs made.In musical truth!Not home theater,as many of todays designs are voiced for.
OK,here are some of my own choices,with the vast majority being heard,by me.Actually all,but the Boulder.
The Boulder is a fine choice,and a class A/B design,which will not run hot.It has a fine reputation,but it is VERY heavy,and this weight factor should be considered in a decision,as you may(God forbid) have to have it serviced or modified,and too heavy "sucks"!
My Rowland(before I had Jeff modify it)was 85 lbs in one chassis,and 165 in the other chassis.I've had it updated/modified about four or five times(it's that good,btw)and now that my son is in medical internship,there is nobody "buff" enough to be of help.BAD!!Think about it!
Other alternatives are the current crop of Pass stuff.The .5 series,which really do sound superb.I heard these,and was very surprised as to how good they sounded(remember,my baseline in amps is a superb,full range tube sound,yet preferrably if it can be had in a solid state design,which completely relies on component mating).
The current Rowlands(300 series) are good,but the older 8 and 9 series were probably their best(if modded to his latest Power supplly technology,IMO).Run way cool,too!
The Dartzeel,which I have heard are superb,but may not be such a great match,as to their 100 watt rating.
I have extensively heard the ASR EMitter,which is a super amp,and has the added benifit of a battery driven pre.I have heard it on the incredibly full range NOLA GRANDS.Possibly the most extended high frequencies I have ever experienced,with this fine amp.Though my impressions(remember only my opinion,soley)were that the other high pedigree Solid State designs were darn close,to the ASR,at the very least.
My suspician is that the Gryphon Antilion Signature would be absolutely "world class" on the Osiris'.I take into account the absolute ability to "drive" the speaker load,with the ability to maintain a stunning level of musical texture,and harmonic naturalness.Like the finest low powered tube units.Not easy!!This is a class A design,and may run(will run) fairly hot.
The Tenor Hybrids are a fabulous choice,and sounded superb,when I heard them.The problem is that Tenor went Kaput,which is quite frustrating,as they were really fine products,and(most importantly)were marketed very heavily(especially by the audio press).Sad!!
Well,sorry for my length,but I am very happy for you,and hope you get the most from your wonderful investment!!

Best!

Bart,you have a superb sense of what you are about,in an audiophile way!I cannot offer anything that would be useful to you,as you seem to have a good feel for what you want to do.That's a really good thing.
You're comment about "variety" is very astute!I do believe this is true,and may be one reason why so many folks have more than one cartridge/arm,or multi components.
My Ascents are underpinned with REL Stentor sub(dedicated room)coming in very low in freq,and with very little gain.This gives me a superb blend,and one Lucien did not feel would work,but definitely does.It really allows the Ascents to be moved out into the room where they stage incredibly well.I simply cannot find a reason to replace them,based upon my listening tastes,and room size.My system is highly modded,and I am quite satisfied with performance.BTW,I am a fanatic about equipment care,and my speakers look about two weeks old.
You're Osiris is another story,altogether.A really stunning product that is really of heirloom quality.The Avalons of that era were voiced to blend well with the Rowland and Spectral stuff,but I have heard Avalon products(from that pedigree)work well with a variety of amps.The sky is the limit for you.
I was fortunate enough to be invited to Jonathan Skull's home a few years ago.He had just gotten rid of his Ascents,for the wonderful JM Labs Utopias.
He had a HUGE NYC loft,and I asked him "how could you get the Ascents to fill such a space",where the Utopias really opened up,quite well.I mean the room was gargantuan in size,and I did not believe the Ascents could possibly be a good match.His response was that they "liked Power",and he used a 400 wpc Forsell amp on them.According to him,they filled that room,but I simply cannot get around the thought.BTW,how did your Ascents perform in areas of dynamics,volume etc when pushed?
To me,the power thing may be important(my room is 22.5x8x13,and not too large),but the TONAL BALANCE,and HARMONIC PURITY of music is what I look to,in voicing my stuff.The best tube set-ups excel here,but some SS designs are no slouches in this area,as of late.You owe it to yourself to hear the ASR!All SS,and not hot running.Very ergonomically appealing for long term pleasure.
I do wish you the best!

Thanks Bart,best of luck!!