Have you tried tube preamps or are you just going off of this site? I have tried a number of tube preamps and solid state preamps and have come to the conclusion a good preamp is a good preamp. One that adds no color of any kind and gets out of its own way. The most important thing I found in preamps is the quality of the volume control and to a lesser degree the input/output stage. I would worry a lot less about tube vs solid state and focus on quality. I ended up with a Benchmark DAC1-HDR and both its analog input and toslink are very balanced (USB is another story) and quiet.
Now my choice in preamp will not work for you but I would demo some tube preamps and see what you think. Just remember that any coloration (distortion) in the preamp section will be greatly magnified by the amps. It is easier by design to make solid state quieter and maybe every more neutral. But tubes can be just as good. But it comes down to what you like. I am not going to tell a tube fan my solid state pre is better... though I am sure he will tell me his tubes are better lol. Now if you think your Magnepans are bright the tubes may just do the trick.
Now my choice in preamp will not work for you but I would demo some tube preamps and see what you think. Just remember that any coloration (distortion) in the preamp section will be greatly magnified by the amps. It is easier by design to make solid state quieter and maybe every more neutral. But tubes can be just as good. But it comes down to what you like. I am not going to tell a tube fan my solid state pre is better... though I am sure he will tell me his tubes are better lol. Now if you think your Magnepans are bright the tubes may just do the trick.