Over the summer we upgraded our 4k Blu Ray player in the living area to a Panasonic Model # DP-UB820-K that is connected to our newer Yamaha THX Select AVR via Optical Audio TOS Link, and the two have never had any communication problems for audio because both Dolby TrueHD and DTS Master Audio that are both considered "Lossless Codecs"
work just fine.
Prior to upgrading, we were using a Sony Model # UBP-X700 that we're now using with our older Yamaha THX Select AVR via Coaxial Audio, and didn't have any problems using those same codecs.
A minor side note: One of the things we love, and kind of hate (yes, it's that kind of relationship) about the higher end Yamaha AVR's, is that there is a menu in them for some of the source inputs where it is possible to choose whether a video input uses one of the Coaxial SP/DIF or one of the Optical TOS Link inputs for audio. This can be a bit of a nightmare when upgrading equipment because it is easy to have to go to the back of the home theater with all of the OCD style, neatly routed cables, and figure out which port option has to be disconnected, then which port option has to be newly connected, and which specific audio input ports are part of the options associated with that specific video input in the on screen menu of the AVR itself. There are times when having to deal with this actually leads to it being a necessary step to do some rerouting of the cables, and is often a tedious process; however it is rewarding upon finishing whatever steps are necessary because it's a "set it, and forget it" kind of deal. This is one of the many reasons we keep buying some of the highest end Yamaha AVR's available because without that flexibility that many other AVR manufacturer's don't offer, we simply wouldn't get the most out of our equipment.
We haven't observed any content on the Roku offering anything except for DTS (by way of the Roku 4640X's settings menu only
) , Dolby Digital+, and Dolby Atmos. To be fair, we haven't bothered looking for a DTS Stream for any apps and services that we use on our Roku 4640X; however Dolby Digital+ & Dolby Atmos, like you said, are not
considered to be lossless.
When we do watch Blu Rays, it is for that exact reason of being lossless codecs we actually prefer Dolby TrueHD and DTS Master Audio over the other available audio codecs that include Dolby Atmos. In short, we completely agree that the lossless codecs are the best available.
The catch is, we still use both Dolby TrueHD and DTS Master Audio (that we prefer over Dolby; especially for StarGate that was one of the first films mastered in a DTS standard, and is such a classic movie that never gets old) over both TOS Link Optical on our newest Yamaha THX Select AVR with the Panasonic Model # DP-UB820-K Blu Ray Player, and via Coax SP/DIF on our older Yamaha THX Select AVR with the Sony Model # UBP-X700 Blu Ray Player that we moved to the master bedroom to replace a Blu Ray player one of us had been using for nearly 10 years, and finally just died.
Anyway, lossless codecs will work over both an Optical TOS Link cable, and a Coaxial SP/DIF cable as long as the combination of both the AVR, and the connected accessory, in this case the two different Blu Ray players we just mentioned, are able to work with the codecs, so it's not an issue of bandwidth or ability related to the cables, but rather an issue of what each piece of equipment is capable of recognizing for the audio codecs that are supposed to be sent/received by each piece of equipment.
Hope this info helps clear up some of the myths that seem to be evolving about TOS Link, and even Coaxial SP/DIF. Independent connections that serve singular purposes will almost always provide better quality than multifunction connections, and that's an aspect of engineering that will probably never change.