do i change the preamp or the speakers?

Good comments by the others. But before replacing anything I would first try increasing the capacitive loading of the phono cartridge. You didn't mention which Shure cartridge you are using, but some of them require significantly higher amounts of load capacitance than most cartridges do. In some cases as much as 400 or 500 pf, which is unlikely to be provided by a typical length of phono cable and the input capacitance of most preamps or phono stages. And even if you are conforming to the load capacitance recommendation for the particular cartridge, going higher than that will likely result in a brighter sound.

DB Systems sells a kit which can facilitate that, consisting of y-adapters and capacitors of various values built into RCA plugs.

Beyond that, and if the issue persists after the new tubes seem to have accumulated sufficient breakin hours, you may also want to consider replacing the cartridge with one known to be brighter, rather than replacing the preamp or speakers.

The first two graphs on this page, pertaining to the Shure M97xE, illustrate what I'm talking about quite dramatically.

As to why you may have found the tonal balance of the system to be acceptable with the added brightness of the Bryston 3B, while being disappointed with the excess warmth you are now getting, perhaps the 3B was excessively bright and was thereby compensating for a cartridge or cartridge loading issue.

Finally, if you do change preamps, in choosing the replacement be careful about its output impedance. Many tube preamps have output impedances which rise to much higher values at deep bass frequencies than what is specified (the specs usually being based on a mid-range frequency). With some tube preamps that will be a problem in combination with the 22K input impedance of your power amps.

Regards,
-- Al

P.S. to my previous post: Here is a link for the DB Systems kit I mentioned.

Regards,
-- Al

Fivefasts, the recommended load capacitance for the M91ED ("N91ED" is its stylus assembly) is 400 to 500 pf. I would expect that under typical circumstances the total capacitance of the turntable wiring, the phono cable, and the input capacitance of a preamp or separate phono stage will be in the vicinity of perhaps 200 to 250 pf or so, and sometimes significantly less.

Some Googling will reveal numerous comments by users to the effect that loading the M91ED with too little capacitance will have adverse effects in the treble region, and specifically that it will weaken the brightness region.

Also, my perception has been that generally speaking Shure cartridges are not known for their brightness. And the graphs I linked to earlier, for the frequency response of the M97xE, are certainly consistent with that. It could be that the cartridge is just not to your liking, and your present system configuration is not compensating for that to the extent it was previously.

Regards,
-- Al