To try and answer your original question... If you are going to go with just one, the general consensus is to go with the preamp. Reason being that the amp can only "amplify" the signal it is sent - so you can induce tube goodness with a pre. Beyond that, a s/s amp offers tighter bass control.
From a practical perspective this does two things for you:
#1 - you can spend less - look at the AES AE-3 for about $400 on Agon
#2 - you don't have to worry about how much poop you need for your speakers, the speaker impedance curve etc if what you already have works well. Also as Gunbei notes, a big tube amp throws lots of heat which may or may not be an issue for you. Since the only way to get more power is to use more or bigger tubes...
From a practical perspective this does two things for you:
#1 - you can spend less - look at the AES AE-3 for about $400 on Agon
#2 - you don't have to worry about how much poop you need for your speakers, the speaker impedance curve etc if what you already have works well. Also as Gunbei notes, a big tube amp throws lots of heat which may or may not be an issue for you. Since the only way to get more power is to use more or bigger tubes...