Thanks for the responses! It seems tubes is the way to go for preamp but will it match well with the B&K amp?
It depends completely on what improvements and sound characteristics you’re looking for. If you share that info you’ll get much more targeted recommendations here. The other thing to consider is you want the input impedance of the amp to be at least 10 times (and preferably much higher) the output impedance of the preamp. This tends to be more a potential issue with tube preamps than solid state BTW.