Actually a ground kit can greatly improve the shift response times on an automatic by ensure that there are no spikes in the power current. I have also experienced smoother reactions for our VDC allowing for a less jerky engagement.

I'm not sure that conflicts with what I said... If the car is already having problems such as "spikes" then fresh wires might be a good choice. But a maintained 03+ car should be just fine. I've heard plenty of people say they "feel" the difference, but this is likely a placebo effect like so many other "mods."

Grounding has been literally debated into the ground, with one side saying they "feel and notice" whatever minor change they claim (but not the added weight or clutter under the hood...) and the other side saying that no test has ever proved a power gain, nor even a noticeable difference in idle/current/etc that's outside the realm of normal occurrence due to environmental variations.

I think the only two agreed conclusions between these sides are as follows:
a)they look pretty
b)it MIGHT be a good idea if you're packing hundreds of pounds of high power stereo equipment into your car. but anyone who is likely isn't worried about optimizing the car's driving performance.

That's my car in the second video , and my homie Jayk, in the first one lol.

I initially bought the Gamma TDX cat-back system from Tony, which obviously doesn't come with the modular XYZ pipe.

Well hey there, hope you don't mind then. I've come across them on more than one occasion (and enjoyed.) I'm actually a Z owner, but my exhaust/intake goals are almost all motordyne and I wanted to hear some sounds myself.

Okay, tell me, because I thought the Gamma did have the XYZ & module. Perhaps it's the non-TDX Shockwave? I know the TDX connects where the module should be, but I've seen pictures of Shockwaves that had dual outs and used the XYZ w/module.

The Gamma mufflers part of the exhaust is just the axle-back, you could use them with either the dual or the TDX. Any non-TDX configuration can utilize the XYZ modules. And, as you know, any TDX configuration can't use them.

And I'm with you on the all Motordyne parts . Expensive, but well worth it.