Good to hear that it's really just the 4 engines. I was starting to worry something else had gone wrong with my setup But now I know. Four seems like plenty, especially given that you can add your own with some hacking!
So my only issue at this point is that I'm not getting any sounds out of MOD-UI. I was at the very beginning of my usage of Zynthian. I then messed with enough settings while trying to get my development situation happening that I somehow screwed it up. To note: I'm able to load the web interface and play around with pedals all day, but I can't get it to produce any notes/sound--even with using some basic examples like the Rhodes and so forth (presets from the Zynthian UI).
Once I get my hardware from @jofemodo, I won't need to have weird dev-y settings, so I should be good to go with MOD-UI.