O2 sensors will throw a CEL unless you either install MIL eliminators, or turn off the rear o2 sensors through a tune.
As far as Sound goes, The debate rages on between x and h. And personally, I think it all depends which catback you go with. Some sound great with an X and not as good with an H. Others sound great with an H, and not as good with an X. Currently I am running an Offroad X with bassani catback and it sounds real nice. Not amazing, but its a nice growl.
I've always been an Xpipe person myself. I do agree Xpipes don't sound perfectly with all catbacks though. Typically, you need to install a chambered catback in order to have an O/R Xpipe sound deep enough, IMO. With the right combo, Xpipes will make the most power and sound great.
I highly suggest picking up a set of MIL Eliminators for any catless mid-pipe. Than you won't get a CEL light and still be able get the O2 readiness codes to set. With a tune, the CEL will be deleted, but the readiness codes won't be set. Thus, you'll fail emissions if tested.
You'll fail visually regardless unless you install a set of "dummy cats" or just tack on a few heatshields to look like cats. This is all just hypothetical of course.
That would depend where you live. Most areas don't require a visual inspection for 1996-present cars. They only require an OBDII check. If all turns out good with the OBDII, than the emissions testing is over. Also, for state inspections, the car does not have to be raised higher than the mechanics waist. He/She, simply needs to check two wheels and two brake systems (diagonal from each other) before lowing the car to the ground. Thus, never even having the exhaust in their line of sight.
I have gotten my '04 Cobra inspected at a Ford Dealership numerous times and have had no issues with passing. The car has LT headers and a catless Xpipe. No strings were pulled or anything to have the car passed.
I'm trying to get a classic muscle car sound out of my 03 GT. I know that an o/r x pipe will put out more performance than an o/r H pipe, but of H pipes, like the pro chamber or JBA o/r H, which ones will have that classic muscle car rumble but still give power