I don't think that's too bad I guess if you're a STAX amp collector, but I haven't heard many impressions of the SRM-300. As to whether that means it sounds bad and is disregarded by collectors, or the concept was too absurd to gain traction, I dunno. But as Mice said if you can get a brand new 2170 set for $479 then that might be the way to go.
May I ask what amp or energizer you are using with those and how much it costs. Would an amp be better than the energizer pretty much always?
SRM-212 as Mice said. I would say amplifiers are better just for the convenience of not having to have two amplifiers to power your STAX. The sound quality of the energizers may very well be affected by the speaker amplifiers, which could be good if you have a really nice speaker amp I guess and bad if you're using a cheap amp. I can't say for sure though, I haven't tried swapping amps with my SRD-7 SB to see.