Wow.
First, I don't work for JRiver, and don't represent them in any way. I'm just another user, and I give my time freely to help people on the forum.
Second, in what way was I belittling IAM4UK, being impolite, or blaming his setup?
I was suggesting steps he could take to diagnose the issue.
If you think there is a lot of animosity on this forum, you must not spend much time on other forums, Facebook, Twitter, or any other Social Media. That is where you will find far worse than just a little animosity. This forum is a very nice, friendly forum, compared to any other I have participated in.
Solving problems remotely via the forum is quite difficult. I know, because I have done it a lot. I don't remember everyone's setup, or how technically competent they are. So I have to start answering questions at some level, and adjust it up and down based on responses. IAM4UK's first post was very good in that he provided some information, and I have seen a lot of his posts, so I know he can handle the suggestions I made. I could ask all the possible questions, and write a book on diagnosing the issue, but that would just take a very long time, and wouldn't speed the process at all. Most often my questions don't get answered anyway, so why ask them?
In fact, it is extremely common for people to have an issue, decide what the cause is (MC27 upgrade) and what the solution is, then come to the forum asking how to implement their solution. It is also extremely common that their diagnosis and the solution is wrong.
Solving a problem involves not only identifying changes, such as an upgrade from MC26 to MC27, but also doing discovery on the whole setup. Even in this case, where the upgrade was blamed, it turns out there was another change, that could be the cause of the problem. i.e. The buffering was changed, which could indicate that the Marantz AVR doesn't like that, although normally the buffer in MC shouldn't cause an issue. However it is possible, if MC overruns the AVR with a data stream it can't handle.
The problem may also only have been noticed because IAM4UK has new movies with DTS-HD MA, which he didn't have before. So DTS-HD MA audio may have always been an issue, just unnoticed.
So suggesting that IAM4UK change back to the setting that caused the problem, so that then some diagnosis can be done, makes perfect sense.
Finally, the "Playback could not be started on the selected audio output" message is almost always associated with the capability of the playback device. When a user isn't Bitstreaming that means settings can be changed in MC to ensure it plays a format that the playback device can handle. When a user is Bitstreaming audio to the playback device, there are few settings to change, as the encoded audio is sent unchanged. But the buffer setting could have an effect. That has to be determined by testing. In fact the first step I would take is to set the buffer back to 250ms in both MC27 and MC26, to confirm the problem only happens in MC27 with the same settings and other conditions.
So, thanks for your feedback Musicmusic. You have been a user for a very long time. How about instead of criticising me, you help IAM4UK solve his problem?