Hello. few points that I thought might help you!
I used to run a set of quad 11Ls with a nad amp and have to say the sound was very very good indeed. Have a look on used NAD 5.1 amps too on fleabay, there are bound to be some bargains that would suit your budget.
As far as underpowering or overpowering your speakers, I'll just say that it is much easier to cause damage to the speakers by a low output amplifier working at large loads, rather than a potent unit, that drives the speakers easily with plenty of headroom. Your music will sound richer with a high powered amp, especially the midrange and bass. The difference is huge in my experience, so if you can afford the 380x series amps go for it! Having said that you do not mention a lot about your connectivity needs, so bear in mind the connectivity to power trade off...

As far as reliability of second hand units is concerned, if you go for a well looked after unit, from a decent manufacturer (NAD, Denon, Yamaha, etc) you should have no probs at all! Of course it makes sense to carefully listen to the amp in various modes when you get it, to make sure that its 100%, but I have bought mostly used items and never had any horror stories to tell. Remember to look after it when you have it yourself too, makes sense for a possible future sale/upgrade!

Finally almost 100% of these AV amps have got NO probs running close to plasma televisions! I have never had any probs with my plasmas and would think that you should have no probs too!
Hope this all helps, good luck in your AV adventure!

Regards, Chris
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My 7.1 System:
Separates: Denon 4308ci,2TB Media Center,BEnq MP610 projector 4m el. screen, LG 50"PC1D, LG DNX190MH DVD,PS3(bluray), XBOX360+HD-DVD drive, Wii.
Speakers: Acoustic Energy, Aelite3 Fronts,Aelite2 Surrounds, Aelite2 Rears, Aelite Center, SVS PB12 Plus Sub in Birch/Maple finish