Well if you want to experiment with a good active preamp it has probably never been cheaper.You can try /buy one of the cheap Chinese clone preamps like the FM Acoustics 155 copies for about $300 on Ali Express.That is s a superb sounding active preamp in my opinion.It may not improve the sound of every power amp because there are always preamp/power amp synergies but suspect it will be a considerable improvement on most .I am talking at least $5000 preamp sound quality.The real thing sold for more like $20,000.
I would normally not recommend things like that but for the sake of killing off the myth that the best preamp is no preamp it is arguably justifiable. I believe that is also an older design on which the patent has expired so anybody can copy it.