I thought I had responded to your post. Anywho, that would be great to have the artwork show up on a per episode basis in the player. It's all in the playlist players on my site and will be going forward. I've got it set up for each category and the main feed shows the artwork now.
As for iTunes and Google Play not showing artwork at the top level; that's fine. I just got a response from Google that they also don't compile all the categories under one main feed like iTunes does and have no plans on doing it in the future. That's odd, but whatever. I've got all the subscription feeds set for both the main and category feeds so folks can subscribe based on their preferences.
Now that artwork and descriptions have been fully updated in iTunes and Google Play by using 6.3 PowerPress player, I have now switched back to the latest version. If you go back and look at all of the category feeds (provided above) you'll see that it has switched back to the main logo/icon for Party Favorz (instead of the individualized artwork for each category) and the main feed description (as opposed to the individualized description for each category). The switch took place last night and so far has NOT affected Google Play nor iTunes. The artwork and descriptions are in tact (fingers crossed).
Angleo, the problem is with the 7.+ version of the player plain and simple. After two days of testing from top to bottom following your guidelines, there is no other explanation. If 6.3 works with ALL of my plugins and my theme and 7+ does not then there is your answer. Remember, I did this last year when I had a different theme as well. It would be interesting to know if the same issue arises with podcast channels but I don't use those.
Anyway, this is my biggest month of the year and I'm done jacking with this issue. I've got a ton of content I've got to get produced and out the door. I hope all of this helped in some way.