having a similar problem to the OP, but I'm using an EUB so not the same amplifying nitemare's. Until I sort my rig out (twin channel bass amp or some other solution) I'm DI'ing the upright and putting it through the monitior's as my only way of hearing it, not ideal, we use yamaha monitors and they are very good for vocals but don't really cut it for the upright, unless you use a very high quality monitor ( my last band used peavey hi sis 2's as monotors, they were superb) I think your going to struggle.