I have looked at a Teensy as well as a Bodnar based setup but I honestly don't know which way to go since I want at least 1-2 sliders in the panel for functionality.
Both cards will allow you use up to 8 analog axis - rotary or sliding potentiometer, contact less sensors.
BU0836 is ready to use controller, besides 8 (analog) axis allow use up to 36 buttons (using POV HAT as buttons) but cost more.
Teensy 2.0 or ++2.00 or cheap (~$5) Arduino Micro allow flash firmware MMJoy2, 8 (analog or digital) axis and use up to 128 buttons, have customisable options and support digital contatcless sensor (TLE5010/11).