What amp is best with Wilson Sasha DAW speakers

You'll not regret checking into Luxman.  It has it all.  

Regarding tubes being better for a transparent speaker, I think lots of contemporary high end tube gear has been made to approach solid state in terms of transparency...especially ARC. 

One the preamp, VTL 7.5 III, Ref 10, and GAT 2 would without doubt all be excellent, but for me the GAT 2 drops out due to being single ended only, and the Ref 10 get canned based on its impedance requirements which mean you can't drive a subwoofer.  

VTL emerges as the top choice among those IMO.

@carey1110

I once had a pair of big Wilson Alexx driven by 2 pairs of D’Agostino Momentum M400 monoblock amps with the ARC (Audio Research) Ref 10 linestage preamp and achieved excellent results. At the time I was using all Transparent Opus cablings, Kronos Pro turntable w/ 12" Black Beauty tonearm, Air Tight PC-1 Supreme mc cartridge & D’Agostino Momentum phonostage pre served as analog front end source components and the DCS Vivaldi full four stacks (Vivaldi masterclock, Vivaldi upsampler, Vivaldi DAC, Vivaldi CD/SACD transport) served as digital front end source components.

I highly recommend the ARC Ref 10 linestage preamp paired with either the D’Agostino Momentum M400 monoblock amps or the ARC Ref monoblock amps for your Wilson Sasha DAW speakers. For digital front end source component(s) I highly recommend the latest EMM Labs DAC or its CD player. ARC & D’Agostino gears pair really well with Wilson Audio speakers combined with Transparent cablings. Ayre, Vitus Audio, VTL, VAC, Luxman, higher end Naim 500 series separate gears will also pair well with your Wilson Sasha DAW.

Remember, your front end source components, whether digital or/and analog front end components, are the most important components in hifi chain.

The Naim 500 series separate gears will also pair well with your Sasha DAW. The Naim 500 series separate gears comprise of the following :
* Naim ND 555 digital streamer/DAC with its external separate Naim 555 PS DR power supply unit (psu).
* Naim NAC 552 linestage preamp with its external separate 555 PS DR psu.
* Naim NAP 500 DR power amp with its separate external 555 PS DR psu.
The NAP 500 DR power amp is a true dual monoural design configurations with left & right channels are encased in separate chambers and are completely isolated and independent from each other with its own independent power supply and voltage regulations for each channel.
These Naim 500 series separates will sound highly musical on your Sasha DAW speakers.

For these Naim separate components you must use DIN connections to connect between components as it will make a big difference sonically, will sound better than using their RCA single-ended connectors. DIN is Naim’s proprietary connectors and is their XLR balanced version.

I am a big fan of Naim Audio. I’m also a fan of D’Agostino Momentum & Relentless series, ARC Reference line, Linn, T&A, Vitus Audio, Tidal, CH Precision, Accuphase, Luxman, EMM Labs, MSB, Soulution, MBL, Audionet, DarTZeel, Burmeister, Chord Electronics, Lamm, VTL, VAC, BAT, Cary Audio, Ypsilon, Ayon, Pass, Levinson, Boulder & PS Audio BHK series among others.

The OP said he cares most about highs and mids. Nothing beats electrostatics when it comes to mids and the air that huge panels can bring to the table. I’ve heard Sasha DAW and Alexia 2 at axpona and In 2 different homes and although they were great in their own right, electrostatics such as ClX art or even neoliths just demolished both Wilsons. You want accurate mids and highs ? Get the CLX. You want big huge sound with incredible dynamics? Then Buy a Neolith. I’ve yet to hear ANY panel he as dynamic as the Neolith. Most shows do a piss poor job with the Neoliths but those who have taken the time to find the perfect amp for them, never ever look back. 
If you are looking for luxman 900u, you might want to talk to Whitecamaross. He has a huge thread here  and has reviewed them extensively. He’s owned those amps like 4 times and has gone through about 300 amplifiers in total. I also believe he owned Wilson Sasha 2 and now own the Neoliths. 

The OP is looking for a lush warm mids and sweet highs. The Martin Logan electrostats do not have warm lush mids and sweet smooth highs, they are complete opposite. I've heard various different ML electrostats ranging from their entry level ESL EM all the way to huge Renaissance. They have very vivid mids and highs very transparent with huge soundstages when paired with the right amps, but do not possess warm lush mids and sweet highs. The ML electrostats aren't right for the OP as he's looking for warm lush sound. Besides, he has already purchased the Wilson Sasha DAW. Now he's looking for kind of electronics that can reproduce full warmth lush mids and sweet highs. 

ML electrostats panels aren't for everyone. I found them lacking organic natural sound and can be somewhat sterile and lacking full bodied and blossom mids. They are too vivid and too transparent for my taste and have somewhat lean lacking full bodied type of sound profile compared to say Sonus Faber, Vienna Acoustics, Magico M3 or M6, Wilson Alexx. ML electrostats are great and perfect for HT application IMO. 

Fyi, every time I did listen to ML electrostats panels they were paired with some big McIntosh monoblock amps and their tube preamps. McIntosh gears are known for their full bodied sound. 

Some people love ML electrostats panels and would discard just about any other cabinetry speakers. My buddy is a big ML electrostats lover and is a huge fan of them. 

I disagree with panels being great for home theater. They are NOT dynamic by nature UNLESS you are talking about the Neoliths. Why would panels be good for home theater when they lack the needed dynamics for movies ? I have tried panels myself for home theater and they didn’t have the dynamic swings that conventional speakers do.
You are right though, they are very real to the source and won’t sugar coat piss poor electronics.
Lastly, I am not saying for the OP to get any electrostatic. I’m saying for him to look at the world’s best electrostatic built today. There’s a reason WHY there is a huge gap in price between the renaissance Logan and the Neolith. I actually went with a friend of mine to listen to some Alexia 2, VR 55s, and persona 7f speakers. The dealer had all 3 of them and there was a pair of Neolith tucked away in the corner so my buddy asked the dealer if he could play them for shits and giggles and the dealer’s words were “ARE YOU SURE YOU WANT TO DO THAT? THIS IS ON ANOTHER LEVEL AND PRICE POINT...” so he proceeded to set them up really quick and plugged in the same amps he had been using for the other speakers we auditioned and the moment the music started to play, I SWEAR I felt like we went from watching a movie at somebody’s home theater to an IMAX commercial movie  theater. The tremendous width, height, huge mids and air in the room was just too much for the rest of the speakers to even compete. As a matter of fact, it was a laughing matter to try to compare because there was nothing to compare.
With all that said, yes to go from the Sasha DAW to the Neolith would cost a pretty penny. It’s not a lateral move financially speaking since the Neoliths are more than twice the price of the Sasha DAW and they should be based on what I have heard.