Just some noodling switching forth and back between the two amps Plex is pure/rough, SB more bassy due to the fixed depth and other other things (loop etc) and cannot reach in ch1 the gain levels of the Plex.
Sounds similar to the differences with the SV20! Smallbox isnt much softer in the top end unlike the SV, but overall a bit darker / rounder / bassier / less clear than the Plex.
I have a ton of amps, including BE100DLX and a WWSB. I honestly don’t know why I need any other amp besides the SB. And a fantastic loop, to boot. Epic in a song and band mix and you showcase the fantastic dynamics on tap.
I have a Plex style amplifier from another manufacturer. it has a switch that adds the fx loop or removes the fx loop. I notice a very similar difference between Plex and the small box.