Most (if not all) professional audiophile equipment reviewers do not believe bi-wiring amounts to anything. If you hunt around the web, you'll find a few fair & objective A/B shoot-outs or comparisons out there where some folks have tested single vs. bi-wire to evaluate the difference(s). The results are largely inconclusive and, essentially, in the ears of the beholders. It's like the age-old debates of whether $5,000 speaker cables are better than $500 cables; super expensive connecters are better than less expensive ones; digital sound is better than vinyl; etc., etc. etc. The standing joke is that "bi-wiring" is just another ploy for "buy wiring".
I had a pair of Paradigm Monitor 9 (original versions) single-wired with 14-gauge Monster speaker cable and then bi-wired them with some 12-gauge AudioQuest Type 4, similar in construction to Rocket 88. Sound was noticeably improved with the AudioQuest. However, I believe this was a function of thicker gauge wire; not bi-wiring.
If I were you, I'd hunt around for a shop that would loan me a pair of 12' Rocket 88 with the dbs (or some other suitable length) and try bi-wiring for yourself before spending that kind of cash. Personally, I'm inclined to agree with those who believe this dbs thing is a marketing ploy. All of the reading and research I've done on this from impartial sources points in that direction.
With respect to the lengths of wire involved, I would keep the lengths identical. I'm not sure you'd hear a dramatic difference, comparatively speaking, in phase response by using different lengths. However, this is a theoretical possibility. Try it. See/hear what you think.