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

I have a Luxman CL38U-SE. It has quite a few functions to tweek your sound. There is a low frequency switch that allows you to select frequencies from 150, 300 and 600hz. High frequency switch where you can select frequencies from 1.5, 3 and 6kz. The preamp also has old fashioned bass and treble controls. I use a Bryston 2.5 SST2 amp. I get a nice detailed smooth sound from my Aerial 5T's.

The brightness on top is distortion (trace amounts of higher ordered harmonics to which the ear is keenly sensitive). Tone controls won't fix it.
Tube preamps make less of this distortion than solid state. For this reason a good tube preamp can tone things down, without a loss of speed or highs.
There are tube preamps that can drive the balanced inputs of the Pass no worries. I'd stay away from tone controls if I were you (and fix the problem instead of putting a bandaid on it)- the more circuits you introduce, the more coloration and less transparency. The reason to go with high end audio is to get closer to the music, not further away!

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.