the guys at
www.Partsexpress.com have some very nice kits. Pretty decent quality stuff with most of the work already done for you. I didn;t see a tower kit, but maybe if JohnA logs in sometime today he can tell you if there is any big stuff. The biggest kit I saw was about two feet high, with two seven inch drivers and a tweeter. You can even download the manual and see if that's the level of work you are wanting to do.
The sub kits and bookshelf kits had alot of options and were very competitively prices. Hopefully John is working on some better center toys and some towers in the very near future.