It doesnt have to be true dual, no. Alot of people prefer the larger diameter single systems for supercharging (nismo, etc).
I'm still debating which zorst to go for, I'm concerned with S/C, HF Cats, and a Nismo, it may be too loud, I,m still very keen on a Miltek exhaust as I know from past experience that (ecu modded) you will get a performance gain and plus they are a bit more subtle, Lomoto, did't you have one?