I put a Dynomax super turbo on mine in October. Not really loud but a little deeper than stock, no highway drone. Certainly nothing like the Flowmaster 2 chamber dual system I had on my 5.4L F-150. If you want loud I'd look more along those lines. Of course it won't sound like your Shelby till you stuff a Coyote in it, which I highly advise.
There are videos on u tube for various exhaust systems.
I have a glasspack on my TJ, I personally love the sound, and a lot of my friends like it too. That is a cheap viable option, other common sounds would be the flowmaster 44 series
Had my jeep since new. 14 years now. When I was younger. 300 miles on the Jeep I had a glass pack welded on and it sounded nice. Deep and throaty. Think about it 4.0 divided by 6 = big cylinders lol. As I got older I picked up a Borla. I love it but it is pretty quiet and you should steer clear. A glass pack is cheap and will give you the wiled sound you want. Plus if you don't like it you will waste far less money.
14 years ago my glass pack was 40 bucks installed. hit up a local shop for that. There welding skills outweigh clamps and crap. Probably cheaper too.
Ps. I would totally go back to a glass pack if I wanted what your asking for. I miss it sometimes.