ARC VT100MK2 substitute

The absolute last problem you have is the amp if you're hearing brightness.

I suspect you have a source problem.

You can save money switching to SS, but I'm willing to bet good money you will gladly go back to ARC after trying SS.

Sometimes people don't know how good they have it (or what the real problem is), so good luck with your strategy.

I have a Pass X250. Previously had a ARC 100.2 which is a really nice amp, but the Pass is much better, at least with my Aerial's. The 100.2 is a SS amp and I'd recommend it highly if that's all the power you need. Agree the VT100 should not be bright but difficult to bias and cost of tubes. My Pass is far from bright. Do you by chance have dedicated circuits with a decent Hubbell receptacle or better? If not; try that first.

I also had an LS-15 and a VT-100 Mk II.
I replaced the pair with a PrimaLuna Dialogue Premium Integrated.  MUCH easier to live with.  Zero regrets!!

I too believe that the problem is not with the AR amp, but with the tweeters in the Focal Speakers.

Before doing something that you may regret, try other amps that are in the similar price point of your existing amp (unless you can afford better).  Listen and determine if that makes the difference you want.  Don't buy until you are sure.  Buying without listening in your system and regretting afterwards really sucks.

I have a hard time believing that the AR amp sounds bright.  Most that I have heard are on the softer side. 

But, some speakers will drive me out of the room.

try to listen in your system first.

enjoy