The Mark IV manual does mention that the Mark IV can be midi controlled. It specifically mentions a midi controller offered by Mesa.
Based on what I have read on other forums, there are some other manufacturers that make controllers that work well with the midi.
For example, I found a couple of quotes that seem to possibly be of help:
In addition to whats been mentioned, you can go with an Axxess CFX4 w/ custom cable for the MkIV and you will have total midi control over your amps switching functions. Of course youll need the Midi Controller of your choice to control it all.
Personally, I think the best bang for the buck is the Voodoo Labs GCX. Not only can you switch a bunch of functions but at the same time, you can run pedals and processors through it. For the price, its a hard alternative to beat IMO, that's what Im doing...
And, the following question was asked:
I thought I read somewhere about controlling a MKIV with a midi foot controller, but I don't see any midi jacks on the amp. I'm thinking about getting one, and sometimes they don't have the footswitch with them used. So I thought maybe I could get a cheap midi footswitch and use that.
and the following answer was given:
Nope, you need an interface to go from midi to relays. The MkIV has a the DIN type input for the foot-switch but that isn't midi. The MKIV has 1/4" jacks for all of its switchable functions and if you want to control any or all of those functions, youll need relays that are midi-controllable. You can find them on some rack processors like the G-Major, Replifex etc and you can find them on things like the GCX or the Axxess box that I told you about.
You still need a foot controller and there are plenty out there, it really is up to you to decide what you want to do with it. I have no need to turn things on or off on the fly so a simple MIDI controller that will allow me to choose any number of presets is fine with me. If you need to turn things on and off, then you'll need something like a ground control pro that has presets and control switches.
These cites came from the following thread: http://www.rig-talk.com/forum/viewtopic.php?f=3&t=23511
Another thread that seemed to be of interest: http://www.harmonycentral.com/forum/forum/guitar/acapella-28/1421006-