Get the mufflers if you like the sound. Worry about the sound later.
Ask the track steward(s) for a free sound check (so that it doesn't count towards your 3-strikes for the day), and drive as far to the right as possible between turns 5 and 6 where the sound check hut is. Floor the car in 3rd gear, all the way up to redline.
Then pit in and grab your dB # and go from there.
If you're over the 92dB Laguna limit, then drive on the leftmost side everytime you pass the sound check hut
- and/or let off throttle slightly just as you pass the hut
- and/or temporarily upshift to 4th, then downshift back into 3rd for the turn 6 and the uphil climb thereafter.
Shouldn't be an issue
My setup is capable of 106dB when I gun it as close to the hut as possible, and as high of RPM as possible, but I can still pass sound check when I do any or all of the above-mentioned in bold.