Only requirement is that it works. Something small, 1 or 2 channel, 15-50W output / channel. RCA in a speaker output (need I say). Those little old Alpine block boxes from the 80's that used to hide in the dash here and there would be fine. Just using it for the voice output of my nav system. Hoping for ~$10 range. I know if I had one that's what I'd be asking!