Oh hello!
My current set up is Bass > HX Stomp > QSC K12.2. I run an XLR from the back of the QSC to the desk. Previously to this I ran Bass > Fishman Platinum Pro preamp > QSC K12.2. Again in this instance also I ran out of the back of the QSC to the desk. One of the problems with using different basses live was the variance in output from each bass, this necessitated different settings for each which had to be adjusted on the fly on the preamp which, frankly, was a faff. I was on the verge of shelling out on a Grace Designs Felix, a great preamp but mucho coinage and only two channels. Now usually I only use a fretted and a fretless live but the fretless has a really hot output and the Godin (the fretted bass) less so, but recently I’ve been using an Ibanez SRC6 as well which kind of negated the Felix, not only that but lately I have been wanting differing tones from each bass for different songs so why bother dropping a grand on a (let’s face it incredible) preamp which is limiting inasmuch as you can set two channels or save myself £600-700 and get a HX Stomp. With the stomp I started out creating three different patches for the three basses. I have ended up with an individual patch for each song! You can set the output level for each bass so when I move from the normal fretted to the hot fretless the patch has a quieter output so the basses are even in output and (obviously) tailor each patch to each song. The Stomp can be your entire rig, I often go Bass > HX Stomp > DI > desk and only bring the QSC if I know the monitoring is going to be crap or if I need to use it as backline. I agree that the volume is a pain being on the back of the unit but with a Stomp you are golden because you set all that in your patches, you can crank the QSC up to a reasonable volume and then tweak via the front of the Stomp if needs be but the signal from all the basses are even due to the individual patches so your output to the desk is even, just set the vol on the QSC at sound check and you are done. I’ll not be going back to a traditional amp/cab setup, the Stomp is infinitely tweakable and through an FRFR speaker it’s just the nuts.
As mentioned before take a good look at this...
...seriously it totally revolutionised my outlook. You are welcome to try my rig out anytime you like.