What does "old but massive" mean? If an option is to link this with your gear then I guess it's a combo.
A marquee is basically an outdoor gig. There are no reflecting surfaces so the bass will get "lost" and, as you know, your bass will need help.
The first option I'd check out, is the PA is good enough to DI the bass. If it is then problem fixed. If it's not then checkout the Peavey and daisy chain the two combos. You're combo can take an extension cab. IMO bass always sounds better with more speakers even when being run at ordinary gig volumes, so I'd suggest getting the extra cab.