I would be surprised if there were a generally accepted value -- they aren't common, and even less so in working condition. And while the powered Advent is a really good idea, its problematic -- the amplifiers age, and can't be used with other speakers and if you have a reciever or integrated amp, rather than just a preamp, the advantage really isn't there, Standard large Advents are common and sound good, even if not as good, but are much less prone to electronics problems, so are strong competition.
So a pair in working condition might be worth a fair amount, but you'd have to find the buyer who wants them -- the problem with all not well known gems.
You will probably get some tut tutting from people who think its rude to ask for values in your first posts, but I think most people first find Audio Karma in the process of trying to find out about their equipment, and price is a major interest. So it doesn't bother me when that's the first question. I do hope you will stay and contribute -- you have an unusual pair of speakers and could be a resource for others.
