Hello caphill,
You have a very good understanding of all the better quality 4K Blu-ray players being discussed. I completely agree with you that the Oppo 205 is the best overall (video and audio) 4K player solution but, at 3x its original MSRP of $1,300 they're presently prohibitively expensive due to Oppo's withdrawal from the player market.
I believe an ideal new 4K player that's as good would need to combine the high quality of the Panasonic DP-UB9000's video performance and multi-channel analog audio outputs with the Pioneer Elite UDP LX500's high quality audio performance and universal disc capability. And, ideally, this Oppo 205 clone would have an MSRP as close to $1,300 as possible, although I know I and probably many others would willingly pay about double that price.
I currently use an Oppo 105 as the centerpiece of my streamlined system and thoroughly understand the high quality audio/video performance and exceptionally high number of important functions the top model Oppos are capable of.
I currently use my 105 as a preamp, a hi-res DAC up to 24 bit/192KHz resolution (I don't even currently utilize its DSD capacity) interconnected via wi-fi to a laptop and 2 TB NAS for a computer audio system, a HT preamp processor for decoding 5.1 surround sound channels outputted directly to multiple amps through its analog audio xlr and rca outputs as well as a universal disc player for Bluray and DVD video discs and CD/SACD/DVD-A audio discs. I'll just have a need for a 4K Oppo 205 universal disc player or alternative once my 65" 1080p Panasonic plasma hdtv needs replacing, hopefully, many years from now. I can wait at least a few years for a high quality 4K universal disc player with 5.1 or 7.1 analog surround and stereo audio outputs to come out.
For ymc226's situation, I believe his McIntosh MX-135 preamp-processor will continue to prove to be more of a system hindrance than a solution mainly due to its lack of HDMI inputs. It was a big,impressive and competent prepro in its day but it's a new day and the future of audio/video is fairly clear. If he doesn't have other components attached to it like a TT, and perhaps even if he does, I'd definitely advise selling it while it still has some value.
If he wants a 4K universal disc player immediately, I'd suggest buying a new or used prepro that accepts HDMI inputs for audio (there's no need to buy one that performs video processing), buy the Pioneer EliteUDP-LX500 and attach its HDMI video output to your 4K hdtv and the HDMI audio output to your upgraded prepro.
Tim