Adding to the OP here, I just grabbed a great deal on this receiver here in Canada on Amazon. It pops up now and then for about $500 LESS than the 3600. Doesn't say refurb, or return or anything, says its from the Denon Store, and SEEMS new, but I'm wondering if it's in fact b-stock return. I wonder this because this price is too good, and it only pops up here n there, then is gone for a while...almost as if they need to get a couple of returns that they'll check over real quick, and send them back on the shelf if they're happy enough with them. If they were returned units that they FELT were good enough to call 'new' but were still returns, they'd have no problem with that price...I THINK...just my idea.
I'm having the SAME issue with HDMI connections. From my receiver rack to my projector I have a pretty good 25 ft HDMI cable that I got from Blue Jeans, HOWEVER it IS about 10 yrs old or more. When I first hooked it up to my sources (PC, BluRay, Bell TV with fibre optic connection, Amazon 4k Firecube) the only things that would NOT show up were the 4k sources (PC and Firecube). The 1080p signals from the Bell TV and BluRay were fine. Then I borrowed a 4k UHD tv and hooked IT up with a 4 ft 4k rated HDMI cable from the Monitor 1 output and the PC hooked up without issue, but the FireCube kept trying to go full HDR and had unacceptable connection...would blink in for a second before blinking back out to "is your source on". Changed inputs on the back to the same result. My conclusion here is that I think it's the HDMI OUTPUT on this receiver that's not fantastic. It's RATED for 8k, but has a hard time sending out a strong 4k UHD signal, even from just 4 feet.
I'm reluctant to send this back because A) it's like a lottery-win to get this at this price ($1200 Cdn, about $896 US) and B) I'm wondering if my suspicion of it being a return is accurate, and will I just get another return?
I ordered a simple cheap HDMI booster for $20 and am getting it today...we'll see if that fixes everything. If not, this unit will have to go back.
Curious if OP had any luck with the Monoprice cable he ordered?