Mcpherson,
Thor has a very very good reputation. If you can get the British tubes into the pre it will make an obvious improvement. I happen to use a highly Modded AE-3 by AES a sub brand of Cary. It is a simple pre which uses 6SN7s, they have great, mellow tone, and are highly linear. It doesn't hurt that I put some very fine, metal base Sylvania 6SN7 "Ws" in it. Thor power amps use EL 34s and would appear to be a really good choice. I have a variant of EL-34s in my power amps, the tetrode 6CA7 fat bottle by EH, which sound really big and powerful. My amps, BTW, are Opera Consonance Cyber 800 monoblocks. The inputs tubes are OS Tung Sol 5687s and Mullard 2493s a 6922 variant. My speaker cables are Jena Labs entry level, which are an all copper braid. The combination is magical.