Ive got a BF 6x4" back box....very pleased with it....but its kind of six and two threes....
Just get whatever you want...you can now also get the CAT back from BF....
BF back box is £155....+if you want the rest is an extra £120 but £275 aint half bad for a system!!!
As i have one, i prefer BF to magnex.......tell ya what i would try to be different is magnex's TRI-OVAL which is upswept too...looks very cool and also the 5" can......im sure they could supply both in universal form....and i know they deffinately do the 5" as a universal fitment!
If i hadnt of gone for the BF i was considering either a 5" round or i do actually think the tri-oval might look spiffing on the ZR...plus i bet NOBODY has that!