Hi.
I don't personally have any experience with any of the Mounts you listed,
But I do Own a CG5 ASGT Mount that tracks very well with my heavy 6 inch refractor and all of my accessories.
Its got an autoguide port, but no Pec.
It can handle the 30+ lbs I have on it very well.

A Losmandy or Titan would be my choice if Money wasn't a factor.

You should look for a mount that has an Autoguide port can run on either AC with an adapter, or DC, has One of the Universal dovetail or saddle type Mount receiver, and will support not only your ETX but a much bigger and heavier load. Pec is also very desirable, (Periodic Error control).
I have heard good things about the Atlas from Orion but I'm not sure if it has an Autoguide port, and PEC as std features.
As far as the LXD75 They may come with both of these features, since they designed the Meade DSI camera with Drizzle technology to work with all of the Mounts they make, but I don't know of anyone in my club that has one.

If you plan on long exposures, an Autoguide port and PEC will make things go much easier.
keep in mind that the longer the Tube the more separation between the tube mounting rings is necessary for improved stability.
Piggy back Astrophotography was how I first started, and I can tell you from experience that differential flexure can be a problem unless you use a Saddle mount or some other rigid coupling from your main scope to your imaging scope, then you will have the problem of centering a guide star thru your main scope, and keeping the image centered in your Camera's Frame.

I did away with piggyback shooting because of this headache, and I now use a radial Offset Guider a Meade DSI One shot color and My CCD Camera all on one scope.
The radial offset guider has two 1.25 eyepiece mounts one of them has a small pick off prism that can be rotated and moved around in the field of view that my scope sees, so that finding a guide star is less of a hassle, and with this setup you don't have to have 2 cameras, you can use a illuminated reticule eye piece and just manually guide while you expose with your camera.
Dennis