Yeah, 350 quid ain´t to bad, especially for these bigger lamps. Especially if they are new. I see the problem that way. The price is more then fair, but out of budget for most collectors, especially as the collectors market for these is limited. And here we are in the difficulty of selling special industry lamps.
You have a very expensive lamp that cost $1000 or multitudes of that. So even you if you sell it for 20-30% of original price you priced out almost all collectors. However who else is going to buy these. With lamps in the area of XBo from 450W-6kW small undependent cinemas do ore event companies how runs the in skybeamers were catastrophic failure is not to problematic. But these are to big for that. Big companies? Hell no, no warranty, no insurance, difficult to buy from private, is the lamp even genuine?
My advise to you is, stick them in eBay and wait. It will take long, and their won´t be an auction war, however at some point in the future somebody will put a bit in.
Dez, if its just for the sack of an XBO, pop me a PN, is still have a few decent one for collection. Not crystal clear but nit black, except you want a heavy blacken does, this I have as well