IMHO, a Bluesbreaker is pretty subtle until it's driven by something else, whether another BB or a boost as you mentioned. If you do use two BB's, I predict you'll want to have both of them on together. If you stack a different boost/OD in front of a BB, you'll have more flexibility. A few of my favorites other than the usual suspects are the Ibanez MT10, the Pearl OD-05 and the Nobels ODR1. First two are very flexible due to their tone stacks, and the third is just a good low-gain OD that stacks well (but does need a bass control, it's bottom-heavy otherwise.)