What Power Amplifier Should I Buy?

It sounds like you don't use much more than 3-5 watts per channel now.  Why would an amplifier much more powerful than the 135 watt per channel amp improve on the matter?  It seems like the only metric people care about is power, so more must be better.  It simply is not the case.  There is much more to achieving good sound than can be measured, whether that measurement is power, harmonic distortion, intermodulation distortion, slewing induced distortion, signal to noise ratio, damping factor, etc.  If if were the case that we can determine quality by any set of measurements, there wouldn't be such a vast array of market choices, alternative designs and fundamentally different approaches to design; things would be narrowed to the objective "best" at each price level.

You should make an effort to hear for yourself an array of amplifiers.  You should not dismiss any type of amplifier based on limited experience with one particular amp; that would be like dismissing all American-made cars based on your experience with a Pinto.  I don't subscribe to the "tube sound" or "tube magic" idea because there is a VAST difference among tube amps (more variability than there is among good solid state amps) and there are many that, to me, anyway, sound more brittle, harsh, and unpleasant than most solid state amps (I particularly don't like most high-powered tube amps employing tubes like the KT88).

I’d look at the VTV Purifi amps.

before you get a new amp consider lowering your crossover frequency to around 70 Hz and if possible and high pass the input to your Bryson at 70 Hz. You can get some inexpensive FMODs from Lincoln Labs to try it out. 

I've had a Levinson preamp (326s) and it did not have the bottom end kick that others do.  It does other things well, but that's not a strong suit.  If the pre is holding back the low end it won't matter what amp you put behind it.

Sub, or better still subs in stereo are going to make a marked improvement in your system. That’s where the oomph is! Cheers 

Your amp MIGHT not be the cause of lack of umph. My recent experience with my ~3 year old Emerald Physics 3.4s (12" coaxial driver) in a large room I long felt that I needed subwoofer reinforcement UNTIL...

This is a mind blower and YMMV (though I doubt It) I recently addeed a single Vera-Fi Snubway (search forum for comments), admittedly plugged into a Core Power 1800, itself plugged into a 20amp dedicated line is, in a word, unbelievable. Since inserting it (it simply plugs into the wall or whatever PLC you might have- MSRP $295!!!) ) I rarely miss having a sub

HTH