I agree with the assessment that the LSI 15 is better than the LSI 25, in many aspects. The 25 can probably produce more bass but it doesn't sound better, IMO.
The LSI line does need good gear and a decent high current amp, I've seen some setup being driven by mass market receivers that don't do it justice.
As for best bang for the buck, here I think you might be able to do better on the used market, with some research and luck. It's hard to get a chance to listen to all the gear that's available used, though, since most of the high end stuff has limited distribution, and not everyone gets to go to CES or THE type shows. You got to listen to the LSI 15 and you liked it, so go with it, I'd say.
The LSI line does need good gear and a decent high current amp, I've seen some setup being driven by mass market receivers that don't do it justice.
As for best bang for the buck, here I think you might be able to do better on the used market, with some research and luck. It's hard to get a chance to listen to all the gear that's available used, though, since most of the high end stuff has limited distribution, and not everyone gets to go to CES or THE type shows. You got to listen to the LSI 15 and you liked it, so go with it, I'd say.