I agree with others that if you aren't loving the sound of your setup, speakers might be the best place to start. But maybe you already know that you love the 805, and you've heard them sound better than what you currently hear.
If that is the case I would say go for the Audio Research but only if you are prepared for the potential hassle involved. Buying an older high-end piece like that is kind of similar to buying an older high-performance vehicle. Both can be rewarding but also both can get expensive when it comes to repairs or maintenance. In this analogy the AR would be an older German performance vehicle. Great to drive but likely expensive to maintain. The Rotel would be a newer Lexus or Acura. Still quality overall, exchanging performance and character for reliability and low cost of maintenance.