Staring at my 4 track, a tascam portatwo, I decided to run my sp303 through the effects loop. Try this if you have not:

My Tascam has a 1/4 on the side for an effects send-run that to sp in.
take the sp out and put it in the four tracks 1/4 effect return(if it is a stereo return-left is usually mono).
Hit Ext. Source pad on your SP and tada-you have a dedicated multi-effect module for adding effects to all your tracks on the four track.

I'm sure this has been mentioned before, it's so simple I don't know why it took me so long to discover it.

How is the sound quality and balance overall?

sound quality is decent, considering. My Tascam has pots for adjusting the level of the effect to each track-so I can dial in a tiny bit of reverb on one track and a ton on another. If you have an effect loop on your recorder, try it. My Tascam is an old cassette version-I'm not sure the new ones have effect loops.