amp/pre combo or integrated for ML's

Hi,
about a month ago I posted for a tube integrated and have been looking for a VTL I85 for a while. I have since heard of some concerns with VTL. While I am still looking for one, I am also interested in other amp/pre combos. Would like to stay with all tube. Recently, I stopped in at a dealer and saw an old Audio Research D-79 tube amp circa 1980. this is a 75W amp that they are asking $1800 for. I am concerned about trying to sell such an old amp. should I be? They also have a Blue Circle BC3 pre used for $1300. I have heard lots of good things about BC's. Also been looking at other Audio Research amps and pre's. I would like to buy used and have a budget of a total of $3K.

Also, could someone please give me a quick lesson on the differance between a preamp and a line stage amp.

14X21 room. Adcom GCD-750 CD, ML SL-3's.

thanks to all (again)
Paul