High end sound

@pointtrucking  

You mentioned that your cartridge has been re-tipped. Has it sounded good since getting it back? If they repaired in any way, it may need a break in period. Most MC cartridges need close to 50 hours or so to sound good. This could also be true after a repair. Re-tips can go either way, some will be improved, some will be as good as they used to be and some can go the wrong way.

You also mentioned new tubes. How new? Many tubes need up to 100 hours of use before they sound like they should. 

Electrostatic speakers often need repairs, something about the ribbons and something breaking down over time. I don't remember what it is, just that it happens. Plenty of folks here will know what I'm talking about.......even if I don't. 

Good luck. I"ve chased things like this myeelf and made many changes over the years. As others have mentioned, our hearing does go downhill over the years and we may never get back to what we remember "in the good ol' days". Best of luck to you. So sorry to hear about your wife. 

Lots of good advice on here- My experience with the SST Brystons is they are unlikely to be the culprit. Because Bryston has a 20 year warranty you could send them in and ask them to be checked as your sound has degraded.  My experience is they have a no questions asked fix it policy. I had an old 4B I took on trade from a buddy that was outside the 20 year window- they re-capped and replaced some switches and something else I forgot about and it was $800.  Since they use new parts and not NOS the unit exceeded it's OEM specs. Pretty impressive. 

My guess is speaker placement and sadly hearing loss. I'm 64 and it's a fact that I cannot hear as well as I used to. Come to think of it- I've more on that list than hearing....

Commiserations 

Must be very frustrating but happily lots of good suggestions and advice, but what will work and what won't will only be apparent when you try them so the priority needs to be what should I prioritise in the interests of cost effectiveness.

Speaker positioning is a no cost option so no 1 in my book. No 2 I suggest is to clean all the connections with Deoxit or similar

Do you have a dedicated power supply to the system? If not and it is an option very cost effective IME.

The amp at 20 years old would almost certainly benefit from a service If it works fine. If not will improve its value for trade in or sale

Cables are never straightforward and can be costly. Finding the ones with the right synergy with the rest of the system needs a home trial but can be very successful.

I can endorse the Goldnote PH10 phono suggestion from personal experience. I had one and now have the PH1000 plus matching PSU.

Hope that helps. Take your time. Patience always pays.

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When was the last time you had a hearing test?  High frequencies are the first to go and can make you perceive your system as dull

Hmm yeah I agree it could be high frequency hearing loss because to be honest, even though I do agree Caps go on Amps, Bryston sound signature is on the sharp bright side of neutral. I do not believe its Speaker height because you have the Magnepans and if you have out 3 feet from the wall as you stated, positioning does not seem to be the issue for the dull sound you are experiencing. Cables could make a difference but cannot be responsible for your system sounding dull of a sudden. Now the combo of a Bryston solid state with a tube preamp I am familiar with and have swapped out the tubes to the point of tedium when I used the combo that was similar to yours. Great fun. It just so happens my Former BAT preamp utilized the very same tubes and I do know the tubes make a huge difference in the overall sound signature. Have you recently changed the tubes or have you been using the same tubes for a prolonged period of time? Have you gone up to the speaker and listened for any strange kind of Whiney sounds/creaking sounds (ie microphoney)? It would be interesting to hear what tube brand you are using and how many tubes the preamp requires.