You don't have to rent xfinity's xFi Gateway modem, which appears to have its own internal PS. You can buy your own and quit paying the monthly rental fee.
I use an ARRIS SURFboard modem (not the latest version) that has an external DC power supply, as do many other available modems made by folks like MOTOROLA and NETGEAR. By purchasing your own modem, you could then use whatever LPS you want.
When looking at the newer modems, I noticed the ARRIS SURFboard SB8200, a DOCSIS 3.1 Gigabit Cable Modem, also provides dual Gigabit Ethernet ports. I will be curious to hear from people who know more than I do whether using the second Ethernet port to send a direct signal to my audio server, separate from the rest of my network, would further isolate the server from noise on the network or whether using an Ethernet cable out of my router to a switch offers the same level of isolation - i.e., is there any benefit to having/using a second Ethernet output from the modem?