4 (well, technically 8) into two doesn’t go without some merging
there is one stereo send FX block, it’s impossible to get around this, if you want to play all four tracks, they’ll all be going through the FX (either L/R or L+R and I strongly suspect e.g. the reverb is not isolated left to right, so you’re likely still mixing/bleeding track inputs)
overbridge and USB won’t change this if you want to use the internal FX
you have to work with the configuration as is
maybe as a compromise record dry directs and also just the (merged)FX returns at mains - all in one pass
this is all well discussed