I have one plug computer and I use this for all-day music player and torrent leecher !
It has only one Ethernet and one USB port. So to get enough storage for music and USB audio card, I have to use a USB hub which has 4 additional ports. The USB sound card is the Creative X-Fi Go Pro which has great sound with the price. You can find it on ebay which is around 18 bucks. The plug kernel should load module sndusbaudio when you plug that USB sound card. To force the kernel always set the default sound card, you have to add this line to /etc/modprobe.d/alsa-base.conf
I have two USB thumb drives. One is from Kingmax, another is from Kingston. In order to get two thumb drives to be automounted, you have to get to Uboot interface. Connect the serial port to the plug, set rootdelay=5 or 10s with bootargsconsole so that the system has enough time waiting for usb_sub starts. All you have to do now is adding mount point for two thumbdrives in /etc/fstab.
The last thing is setup mpd on the plug. The mpd client I use for mobile is MPDroid which has great interface.