the borla kit that comes with the SVO has a design where it comes back on itself, so the muffler mounts in the stock location, then goes forward to exit at the door sill. I haven't been under mine in a while, but I think the sub frame of the IRS gets in the way of where the muffler mounts. it wouldn't require anything extensive, but I didn't want to cut up something so nice. I will try to take a peek under there and confirm.
I seem to recall one member on here that had the SVO's and an IRS though... and the subframe does mount right where the LCA is on a SRA.... maybe I'm losing it.