The LS-2B on the used market ($700-950) is an outstanding value for the money. I've had one which I've kept through several different amp changes in my work system. It is a hybrid design using a single 6922 tube. It is very sensitive to tube changes and consequently will sound better with a good tube in there. I've tried many varieties and have come up with some fairly obvious conclusions: Favorites are Siemens CCa's, followed closely by Telefunkens (also the A-frame version), then Mullards. I've also tried Amperex (70's version - OK) and Sovtek (awful). My buddy has an LS2B that he's using the Soviet-made Rocket tubes (I think they are 6H30's...is that right?) and he says they sound great and he had rolled them against a Siemens A-frame I'd loaned him. I have yet to hear those tubes myself. My LS-2B has been modified by Steve Huntley at Great Northern Sound http://www.greatnorthernsound.com. I had him do his Standard mod on my unit which I've wrote about in other threads. In short, it is worth EVERY PENNY and brings the performance up to a markedly higher level - I've directly A/B'd mine against my friends stock unit with all other parameters identical and we both agreed immediately on that point. Steve also offers a "Reference" mod at about twice the price. My bet is that it would be worth considering as well, but is twice the price of the standard mod. Still, the stock unit remains an excellent sounding pre and is definitely worth it's asking price. Steve (Huntley) worked for ARC for many years, then went to WADIA and now has his own company, GNS. In my conversation with him on the phone he opined that the LS-2B was already one of the best pre's ARC made short of their Reference line. I've used it with several different amps and synergy was excellent with all but one. At home I have 300B SET amps and with those amps it tended to sound too cold and analytical...it took away some of the air and magic that I am used to with those amps (I otherwise use a Cary SLP-50A with those amps which is an excellent match, and is an all-tube design - stone simple with two 6cg7 tubes....a real sleeper of a pre-amp IMO). With everything else I've paired the LS-2B with it has matched up well. Those amps are: Mesa Baron, Quicksilver Silver 90's, Quicksilver EL34 Triode prototypes, Pass Labs Aleph 5, and Quicksilver Mini-Mites. Needless to say I am also a big fan of Quicksilver products. The LS-2B has the option of using a balanced "Direct" input (there is only one, so you can only run a single source this way, or swap out the interconnects if you wanted to run a different source), which bypasses some of the circuitry and gives the signal a more direct route to the output. I have found this does give you a definite, albeit marginal improvement with added clarity and focus. All of the other input options are strictly RCA's, while it has both RCA outputs and two pairs of balanced outputs (hence the "B" in the model designation).
Hope that helps.
Hope that helps.