From how I read his post, he already had the XL4 in his house and later decided to buy the 720p TV for his bedroom along with the mini and MoCA adapter, so I see no reason why he wouldn't have had ethernet already connected to his XL4. Perhaps he can comment to clarify? If that is the case, then there was no need to get a MoCA adapter UNLESS
he didn't have it connected to his XL4 and when he added the mini he had an ethernet drop close by and used that spot as the insertion point, since the mini won't act as a MoCA bridge, he needed the adapter.
I probably wasn't clear, but what I meant by saying I thought it was a "bandwidth/speed issue", I should have added the word "error" in there. I know MoCA is more than capable of handling it, when it's working properly. I was thinking it sounded like it may not have been (bad splitters, amps, barrels, taps, drops, etc somewhere in the line) working properly. As an afterthought I also think it could be that he may need a MoCA filter, which without one can cause macroblocking, pixelation, etc.
I'm with you on the scaling issues!
Sorry I wasn't more clear and thorough. I hope I made more sense this time?