Wotcha and welcome Owen,
removing the box and panel and replacing the lot with a cone and larger tube will give you a little more induction noise, do you have any sound proofing on the underside of the bonnet - if so you could remove that and get a slight increase in overall volume from the engine.
You have named some top recognised aftermarket parts suppliers so I would say it would be more down to personal taste for looks as much as anything else
I believe they do have two cats in place as standard a straight through pipe will make it louder but with the sound different exhausts will vary the tone you (again down to personal tatse) tube will give you an idea and we have had some baffle in baffle out vids posted on the forum but be aware some of the members describe rattling neigbours windows and light fittings so the potential is there should you want it.
I would recommend getting a map done to complement any changes you make to teh exhaust and induction side of things.
it has been discussed on here about recirc vs dump valve and the dump valve will give you a great sound (again we have threads with vid links to different valve sounds or you tube search) but will cause the car to run rich momentarily resulting in some flamage in the exhaust :P a recirc will do the same job but without the fuss so again down to personal taste
One thing I would say before you spend loads on aftermarket goodies check you have a good foundation, good recently changed oil, filter and plugs as you could be bolting things on and not achieving the results you would like