Craig, forgive me if I seem like a jerk. I'm really just trying to HELP YOU. But, you have to help yourself. You need to put in the effort in reading manuals, Googling the shit out of all these little problems, and plugging shit in every possible way to see what sounds good and what doesn't. Your going to be in way over your head if you don't put in the effort.
The pdf manuals for any of this gear is available from the manufacturer as a free download.
As they said above, the rack wah you want to buy doesn't have MIDI. It is controlled by an expression pedal with a TRS cord that plugs into the back of it. It uses control voltage (not audio or MIDI) to sense the pedal position by sending a small voltage from the rack unit, through the pot in the expression pedal and back to the unit.
There are some boxes that will convert the MIDI to CV for a couple hundred bucks. Not sure how well it works, but a search will bring up some info. I would just run a 25' TRS and call it a day.
http://www.kentonuk.com/
There are also some MIDI wahs available.
http://www.glab.com.pl/wowee-wah_en
http://www.prostage.eu/remote-wahwah.html
Your question about gates can only be solved by experimenting with your gear. Does it currently work the way you want it? Decimator pedal in front of the amp and the DBX in the loop. If not, replacing the dbx with the ISP pedal with dual ins and outs or the the deluxe rack model should fix your problem, unless you have ground loop issues somewhere. If so, some ground lifting or isolation transformers are in order.
In your original thread you mentioned that you use a 6534+ head. These are channel switching heads, right? Why would you not want to use that? All dirt all the time? Alright. That's cool. Just be aware that some years of that amp used a 5-pin DIN jack for the switcher pedal. This is not a MIDI jack even though it looks exactly like one. A custom 5-pin to 1/4 y-cable would solve that fiasco.
Your the one who wants to build a switching rack. Show us how it's done.
