If you want a really loud exhaust then you shouldn't have started with the Milltek really...
I have Berks HFC's on my Milltek and it is just right, absolutely no drone and nice and quiet when cruising on the motorway or round town, must a really nice bark and grumble when you push on a bit
Best thing is no worries about MOT's etc.
If you are anywhere near SE London then you are welcome to a listen