Mini on a switch
Here's my experience...
I have had a Roamio and Mini for about a year. When I first installed my Tivos, the Roamio was connected to a WD MyNet 8-port GigE switch which was connected to a Linksys SE2000 switch that then connected to my router. The mini was connected to a Linksys SE2000 that connected to the main SE2000 in front of my router (i.e., both the Roamio and the Mini ultimately terminated at the central SE2000). So my config looked like this:
Roamio --> WD MyNet --> Linksys SE2000 --> Router
Mini --> Linksys SE2000 -----^
This configuration worked pretty well, but I got brief 1 second audio drop-outs periodically - about 1-2 an hour. About 3 weeks ago I tried to get rid of the drop-outs by replacing everything with Netgear switches. I put a GS116 in front of the router, a GS105 on the Roamio and a GS108 on the Mini. So the config looked like this:
Roamio --> GS105 --> GS116 --> Router
Mini --> GS108 -----------^
My drop-outs then increased to about 1-2 per minute, with several instances of "network too slow" on all HD programming (both live and recorded). After changing all cables, eliminating the GS105 and GS108 and various other troubleshooting efforts, I found that the issue was the GS108. For whatever reason, the Tivo Mini just did not work well with it. I took it out and replaced it with my old WD MyNet switch. This switch provides "preferential" ports that are higher priority than others on the switch. I plugged the LAN line into the slowest port (the red one) and the Mini into the highest speed port (the green one). This appears to be working well, with no drop-outs on recorded or live TV (so far)! As an aside, my receiver, an Integra DTR 50.2, was a bit finicky on the Linksys and Netgear switches as well, refusing network connections and/or dropping the connection to Pandora periodically. The WD MyNet seems to have resolved this as well.
So, bottom line, running the Mini through a switch works fine, but it has to be a particular type. I wish I could tell you why and which other switches work, but alas I cannot. I can only say that this config works for me:
Roamio --> Netgear GS105 --> Netgear GS116 --> Router
Mini --> WD MyNet -----------------^
A couple of interesting factoids:
1) When I bypassed the Netgear GS116 and plugged the GS105 and GS108 directly into my router (an ASUS RT-AC87U), the problem got even worse.
2) By connecting both the Roamio and the Mini to the same switch (GS116), the router is essentially taken out of the picture (pun intended). It is used for DHCP and Internet access, but the streaming between the Roamio and Mini takes place directly on the switch. I can actually turn off the router while streaming or watching live TV on my Mini and the video/audio continues. This is obviously what a switch is supposed to do, but it just didn't hit home until I tried it.
I hope this info is useful to you and others that may be in the same situation.