Upgrade preamp?

AVM has a tube output stage in its PA 5.2 and an output impedance of 100ohms.  This lists for $5500 and could be a very interesting unit at the high end of your budget.  This is an extremely smooth sounding and enjoyable preamp.  For jazz, it would be brilliant.  If you like a tube sound but need SS performance, this could be an amazing option for you.  
There is a new AVM PA 30.3 coming out in the next two months or so and have an output impedance of 50ohms.  This thing is feature packed!  Obviously I haven’t heard this yet but I have yet to hear anything from AVM I don’t love.  
The Musical Fidelity M8 Pre has an output impedance of 47ohms and is just under $5k list.  MF is known to be very Musical and a strong value since it is made in Taiwan.  
At a lower price, the M6s Pre also has an output impedance of 47ohms and at a list of $1900 represents an amazing value.  
These  should work with you Bryston amps well.  These are neutral to slightly warm in sound profile. 
If you would like to discuss further, want the manuals or need additional info, feel free to PM me. 

Thank you jjss49.  The Conrad Johnson looks like an interesting option.  Funny you mention the Herron as I was looking at one yesterday.  I've never heard one and the lack of reviews makes me a tad nervous.  

@georghifi, i read that you want to have a minimum of a 10x different between your preamp output impedance and your amps input impedance.  My current Freya+ has a 600ohm impedance in bridged configuration.  The 7.5kohms of the Brystons exceed that but I'm sure it's far from optimal.  Would you recommend trying to at or under 100ohm for the preamp? 

@adg101, I completely agree.  I priced out the 20.7's had my current listening room would accommodate a speaker of that size  but I'm contemplating a move in the next six months and don't want to commit to a speaker of that size and investment until I know where I'm going to be long term.  In the meantime, I thought I could start upgrading the rest of the chain and when I do settle down I'll be able to get the most out of the upgraded speakers. 

Thank you Verdantaudio.  I'll give the AVM PA5.2 a close look.  Appreciate the information and will certainly reach out with any questions.

Thank you all.

Mike 

Cayin SC6 dual mono @ $1500, best bang for the $

Brother, if you've got that kind of budget(2 big Bryston amps and then up to 5K for a pre)  you should be going straight to a high end audio shop that carries the Maggies and amps/pre's  that complement them.  

The Prima Luna Evo 300 and 400 series preamps have I believe a output impedance of 256 ohm’s. They will work well with any power amp. Sound fantastic too...