Hey Stuart - in the UK if someone sells you something that proves defective almost from the get-go, you have a legal right to have it replaced (not repaired) as the goods are considered in UK Law to be "not of merchantable quality". I'm surprised this doesn't also exist in the USA - generally the UK is behind the US on matters of consumer rights and protection. It's a real bummer for Theresa - she's only had the 4311 for 5 minutes and having to have it repaired, even under warranty, is real bad news. I really feel for her.
I ran into a similar situation recently as I was looking to get a second new, not refurbished, Denon POA-A1HDCI for my big system (which currently has a Denon AVP-A1HDCI and POA-A1HDCI). The intent was to be able to bridge all channels in my system - I currently have the front 3 bridged and am using a single channel on the POA for the sides and surrounds. I contacted the AVS Store and after calling Denon, they told me that Denon had 1 more available in their warehouse, so I bought it. When it arrived the warranty paperwork was for a refurbished / B-Stock unit (1 year instead of 3) and upon taking a careful look at the amp (before taking it out of the plastic), there was a "Refurbished - Warranty void if removed." sticker on 1 of the screws on the bottom of the unit. It also arrived with some cosmetic damage (both handles on the back were bent). I contacted Denon and much to my surprise, they couldn't give me an answer right off the bat whether it was truly a refurbished unit or not based on the serial number - they gave me a case number and promised to call me back (yes, I held my breath). I contacted the AVS Store and let's just say they were NOT happy with Denon. I've been issued a full refund (including shipping) and Denon is supposed to be having UPS come pick it up. Normally I would just take something like this to UPS myself, but it weighs 150lbs and I think I'd have issues getting it into and out of my vehicle and I'd also have to enlist the assistance of a friend to help me with it. I'm obviously disappointed, but I can't complain with how AVS handled this - they were a class act in giving me my refund before the amp was on its way back to Denon. It's still sitting in my garage waiting to be picked up. Since no more POA's are available, I'll have to stick with what I currently have or take a look at other options.
If you have any suggestions of what change to make that might make it work then please make them. I've tried every variation that I can imagine. I've even tried a WD TV Live instead of the Roku, the problem persisted. All worked with the Onkyo. I continued to try variations for many hours until I ran out of them. No, I don't want to pay $1300 for a receiver that will not pass 1080p60 even though its not "necessary" and has work arounds. There are very few new features with the 4520 that I will use, perhaps the networking and Spotify. But at least it will have the features that I see as essential, including 1080p60 which I would insist on with even a $400 receiver.