I don't see this working out for you.
The secondary cats are made of a metal honeycomb, rather than the more common (at least in my experience) ceramic honeycomb. Point is that you can't drill them out ... and yes, I tried.
Even so, if you were able somehow or another to drill a hole thru them, you are just going back to, effectively, the straight pipe that you have now. The exhaust gas will seek the path of least resistance, which in this case would be right thru the hole. I don't see any gas willing to work its way into and thru the remaining honeycomb if an easier and less restrictive path exists.
Seems to me that your best bet is to keep your test pipes as they are and just put the stock muffler back on as a trial, if you think that your aftermarket muffler is too loud for your taste.
Good luck - DM