I have 2 XG1's with Tivo and 2 Tivo Minis. Each Mini is going to its own XG1 Box.
I have Coax from street ->4 Way Splitter->(Line 1) XG1, (Line 2) XG1, (Line 3) Tivo Mini, (Line 4) 2 Way Splitter [line a-Tivo Mini, line b-Netgear MOCA Bridge->CableModem]
The connection doesn't drop out or lose internet. Haven't really had problems with the Minis talking to its XG1 counterpart. I can watch Live and Recorded stuff with very little problems. There is one issue of screen frame skips. This doesn't bother me too much when watching slow moving things like sitcoms, news etc but it's pretty much unbearable trying to watch sports. The picture is great, it just seems to either skip a frame or lose a frame ever few seconds. It kind of has a human blinking effect when you close your eyes. If you look at something stationary on the screen, such as an NBC logo you get see it get pixelated for a frame and then go back to normal. This happens about every 3 seconds or so. This blinking / frame skip is consistent on both Minis connected to different XG1s on both recorded and live tv.
Moca settings show 220-250 MBPS in PHY values. Not sure what these are measuring to tell you the truth.
My only bet was needing a POE Filter which I ordered online the other day. But that didn't help at all. The splitter is only rated for 1ghz but must be working enough to get that PHY values above. People say anything over 200 is good.
Tested a different router and same thing.
Maybe some weird interference things.