Today, I spoke with an Acura factory rep; hitch mfg. guy; Acura regional service rep; Richardsons' RV; and a hitch distributor. Here's the deal as I now know it:
There are several overlapping issues:
1. The MDX has a 5k# towing capacity, but the hitch is limited to a Class III (4K# capacity) only. As you all likely know, if you add a WDH to Class III hitch, it increases its rating to 5K#. BUT, Acura "recommends" that you not use a WDH and that gives you a big disconnect between their advertised 5K# capacity and their "approved" 4K#. To me, this seems to be an issue of false advertising, but someone else will need to fight that battle.
2. According to Honda, the issue with the WDH install is twofold. The underframe of a Unibody constructed vehicle has nowhere near the strength of the old fashioned frames most of us grew up with. This means that a WDH could possibly add enough leverage to twist the frame. Acura says that the second issue is that the MDX pulls more from the front (even with AWD or 4WD) and that, too, can cause issues with the WDH. (I don't know . . . I think I stopped listening after the part about the frame twisting.)
BTW, the Acura factory rep said that he has photos to prove the twisting, but is not allowed to share those. The conversation was recorded with full ID given on both sides (including my VIN) and documented with a case #, so I have no reason to doubt him.
Acura also says that the installation of the WDH in itself does NOT void the warranty, BUT if there is an incident that causes the frame to twist, then that would not be covered by warranty.
3. Acura dealerships can install Class III (2" receivers) only. If you decide to go the Class III with a WDH route, it will need to be done by another shop.
4. Then there is the issue of the Acura tow package component of the Vehicle Stability Assist (VSA) which I mistakenly called TSA in an earlier post. The manufacturer says that the Equalizer with 4 pt. sway control will eliminate the sway that causes the VSA to engage. There is also a switch that can turn it off.
All of the above was confirmed by the hitch distributor, etc. Richardson's double checked my research and confirmed what they could and were surprised at some of it; the Acura service guy was a bit clueless but knew they could not install anything other than what is listed above; and the Acura factory guy listened, understood, had experience with, and was able to explain all of the above from their POV and their policy.
Bottom line: As many of you have already decided, we are installing the WDH (Equalizer 600/6000) on the Class III hitch and moving on. We will be very careful to stay well within our weight guidelines and distribution and cautious in our near term driving.
There is definitely a new TT and a new TV in our future. If you are in Southern California, be on the lookout for an x20e with a renegade Beagle aboard. The refreshments are on us, but remember we can't tote a lot of beer as long as we are towing with the MDX.
Thanks for your help and I hope my research and posting has helped someone else.