When I bought my XRK, transmission was 2 qts low, leaking from an electric connector, operating on brown muddy fluid. Also, I had occasional erratic transmission behavior, on top of bumpy shifting from 1st - 2nd, both of which had slowly disappeared after I drained and refilled transmission with 2-3 qts of new fluid at the time, about 4 times total. First time I was using cheaper Valvoline ATF +4 fluid.
After running ATF+4, for ~2K miles I was pleased to find out that fluid was rather clean and still very much reddish, rather than previous muddy brown. New transmission filter was still clean, with white fiber showing from the opening. Most pleasant news was very little accumulation of metal fuzz on super strong magnet, that I installed 2K miles ago in the transmission pan. So, ATF +4 is ok for W5A580 and it caused no harm, but good to my XRK. Yes, I am happy that I did not pay some insane money to Jaguar, or any other dealer for "dealer suggested fluid". But this time, I am using Amsoil fluid, as permanent, which will take 3 drain and fills, over time. Today was my first gallon of $8/qt, Amsoil Multivehicle fluid.
Here are some pics, that do speak for themselves.

 

It's good to hear that at least one person has reported success with the ATF +4 as it is commonly available.

There is another suitable Valvoline formulation for the 722.6. Valvoline Maxlife ATF. It usually sells for about 2/3 of the Valvoline ATF+4 pricing. There are notes about it's suitablility in the Mercedes forums, including documentation. They, of course, have a far larger number of vehicles with the same transmission.