Nope, nope, nope!!! AT-P is a single frequency machine that uses software to help compensate for the conductive salt. Think of it like putting traction control on a 2-wheel drive vehicle that is going through mud or snow. Meanwhile, your E-trac uses multiple frequencies simultaneously to compensate for the salt as well as software to further refine the process. So the E-trac is like 4-wheel drive.
If you run the AT-P in salt, you will have to constantly ground balance. You will need to reduce sensitivity that results in dimished capacity to find small and deep targets. In areas other than pure white sugar sand, you will typically hear excessive chatter. Since you are already spoiled with a very competant machine (Etrac) I think you'd find the ATP absolutely unbearable. All of these negatives are the same for single frequency detectors such as the MX Sport, DetectorPro, etc.
So for about the price of a AT-Pro, consider a Tesoro Sand Shark PI or Garrett Sea Hunter PI. The surf (or deeper) tends to wash away the light trash that you'd typically find in the towel areas. So yes, you can't discriminiate, but you won't be finding as much trash either.
For slightly more you can buy a White's BHID which is a dual frequency VLF that works great in Salt water and lets you discriminate. The difference between the BHID and the Excal or CZ is that the BHID has a manual ground balance where the others are auto GB. In dense black sand, it can be a challenge, but for most areas, it works like a charm.