I used to own the Boulder 866 and just acquired the Luxman 509X. They are both stunning! One is not clearly superior over the other and it comes down to preference and synergy. Luxman has a cleaner, more precise sound, lively, and pretty juicy. Boulder is a bit softer, smoother, but very authoritative and still very detailed, and I think has a slightly deeper soundstage. The price difference is about $4-5k used or new, but the Boulder has a really great streaming DAC built-in, which is probably in that price range if not slightly above in terms of performance. The question is: Does the complete package match your taste? With the Luxman you can explore the many options out there for external streamer/DAC, but then you have added cost of cables as well.
One downside to the Boulder is that there is no IR remote, only RF.
Are they overkill? Maybe, but I have no doubt will sound great and either amp will extract the best from your speakers, which you can upgrade later.