@bobheinatz I have the Boulder 866 in a simple system with the Project RS2 CD Box transport and Joseph Perspective2s. I just initiated a cable upgrade with a similar budget. I have tried a number of different power cables with the 866, including an older Elrod (my favorite with my previous amp), Core Power Diamond Extreme (a relative bargain), Audio Envy Whale, and a few others. Two weeks ago, I ordered a Hijiri Takumi power cable. It is still settling in, but was a substantial improvement from the get go (which, given the price, was a relief). My investment in the Takumi followed a review of the various threads, talking with Colin, and also a back and forth with another Audiogon member who had tried the Takumi on his 866, with great effect (as he told me, "Believe me, there was a big part of me that kind of hoped it would just be another overhyped cord, but its impact was just undeniable." I concur).
For speaker cables, I have been using the Silversmith Fidelium. I love them, especially at the price, but they may be a bit light on the bottom end. I am currently in the market for an upgrade. I just started an audition of a set of Argentpur cables made by Ernie Meunier (https://argentpur.audio). I think they may be what I'm looking for, but I haven't had time to assess them yet. Another cable I was looking at is the Inakustic 4004.
I use an AES/EBU from the Project to the DAC in the 866. I don't know if you need a digital cable. If so, I've had great experiences with both the Hijiri Million, and also Bob Grost's Cerious Lumnsicate cable.
I hope this helps. Good luck in the search!