If you are looking for a Raspberry Pi solution, you can solder the SIO connector to the GPIO pins of a PiZeroW and run RespeQT on it.
I recently got an 800XL as well, I got a U1Meg, Stereo Pokey from Lotharek and a UAV from Bryan here. The UAV hasnt arrived yet (doesn't ship till Nov) but the rest is all working. When SIDE3 comes out I will probably get one of those as well.
If you aren't getting into the homebrew scene and programming and you only want the 800xl for games, you really only need the "sio2<something>" device.