Tube Pre-Amp, vs Solid State with Tone Controls/EQ to take edge off the top end?

one of those threads where everybody might be right..
bad power does not help
distortion is bad
maybe the Thiels are a git bright w rising top end, certainly not an odd observation as even die hard Jim Tbfans notice this sometimes ( count me as one and an ocassional owner and I used to sell them ages ago
maybe it is the room
and maybe it is the recording.....where tone controls are a god send....Gold Dust Woman..might be a fair example...

Don't tone controls introduce phase problems? Simple circuits mitigate phase problems?  And how does one detect how much phase accuracy influences realism in the sound reproduction.?

Generally speaking, its best to avoid ...
using Tone Controls unless it is a well-reputed high end audio piece. 
Luxman, BAT, etc

I thought Pass made an Integrated 250w amp?

--SimAudio, they make high-end integrated. 
--Rogue Audio, Vincent Audio: both great 
--Quad: came out with a 80wpc (gorgeous) tubed integrated about 8 years ago or so. 
--oh, NAIM! the SuperNait II or maybe they have another high-ender now.
--Pathos are well regarded hybrid tube/ss integrates. Great for most all types of music. But you may want to Bridge their amps, which I've read is the way to go.
Hard to tell since you said you would not reveal the speakers. 

But lets get back to the basics: dirty electricity and distortion.

The lesson learned here is that using cleaner electricity UP FRONT and better POWER CABLES up front that run from the wall into a power isolator (I use a Pole Pig- 8 ports) and/or a conditioner (I use a Shunyata hydra 2port). 
- I heard improvements with every up grade.

**But what really blew me away was my last change:
Changing from a respectable Belden ethernet from Blue Jeans Cable to a Wireworld Starlight into the ethernet renderer.

**After I changed to the Wireworld, all and all grain went way.
The soundstage grew larger, while the musicians came into much better focus, and the PRAT just snapped into place. 
So I cant blame the amp or speakers anymore. 

@almarg for the win!  I was reading through this post, thinking a DEQX would solve this.  I too faced the same issues with “awkward” high end frequencies, too bright, but not consistent.  I say “awkward,” because the high end wasn’t consistent on every type of music I listened to.  Sometimes it would be inline with the overall track and other’s it would sound “excited” and cut through the rest of the music.  Sometimes it wouldn’t be enough.  I thought, ok, it’s got to be the room.  Had GIK Acoustics build a room treatment setup, based upon my room dimensions and outputs from REW (Room EQ Wizard), which helped, but there were still some weird high frequencies popping through.  I toed the speakers in, moved them away from the walls, spent a couple months monkeying around with placement.  Then thought, must be the tubes in my preamp.  Bought NOS Mullard’s, frequencies still there.  Additionally, I had an entire Shunyata setup, power cables and conditioning, then someone recommended a DEQX.  Solved.  And when I say solved, I mean, it elevated the entire musicality of the system.  They are pricey, but can be had on the second hand market and there are folks on here that really know how to squeeze the most out of a DEQX.  

Best of luck in addressing it.