ouch, just drafted a major response to everyone and got a time out error!
summarising:
1. Colterphoto states 3000 ft3 as optimum for THX system, I have 1500 ft3 so that doesn't look so good. I'll call him direct and ask advice.
2. Reboxing to avoid VAT and duties works really well, but for this quantity of stuff it would be unusual for customs not to get suspicious, or they would at least want the sender to list the contents. It's risky. Better is to find a reseller willing to put a lower price on the paperwork, but again, this is assuming the customs doesn't think to check the prices on the net.
3. Temp range here is -5 to +35 degrees centigrade (I'll let you convert to olde worlde units I could mount the speakers on the wall without any problem and would have to do that for the rear surround speakers anyway. Front speakers can be floor standing or wall mounted. The walls are 40cm thick and plastered with cement/lime finished in pure lime skim, then painted with eco clay paint. I'm expecting pleasant accoustics, however was also expecting I will need a few accoustic panels to balance the sound.
4. RF52's, ok will take a look. I wish there were a Klipsch dealer here (Slovenia). I found a guy who will bring kit to the house so we can audition different stuff, but he doesn't have any Klipsch. It was reading about the THX system that originally turned me on to High End HT, however, we do have some good stuff here in Europe I'm told.
Thanks again for all the comments
edit to add:
Found a dealer in Germany who can supply the THX 5.1 for 5k Euro, that's around $7,500, so price is coming down all the time
He recommends this receiver to go with it and says it's the best sound he's heard for the money:
Onkyo TX-NR 905 http://www.eu.onkyo.com/products/product_en_2008_5875718.html