A lot of lights with sound active modes behave mad/fast when in sound active mode. Sound sensitivity refers to how much or little sound it takes to trigger a sound active trigger, not speed. There would need to be a secondary control for speed.
I don't know exactly how they operate or what the chipset instructions are, but I bet it's something like running a random number subroutine with a limit of 0-255, and once a pan and/or tilt value has been generated, once the trigger is activated, it moves to that position and generates a new number combination for the next move
I'd say the best way to control this is to use some sort of software or hardware controller. Using MyDMX, you can generate your own patterns and control speed, but you lose the sound active capability UNLESS this light has sound active in the DMX traits. Of course, if you throw the fixture into sound active via DMX, you bring up the same issue again. Using MyDMX you lose any sort of "chase to sound" functionality, but that's a limitation of MyDMX, which for me hasn't been an issue. You do have to "hard code" the time between steps and/or fades, but they can all be adjusted whenever you want.
Using a hardware controller like a DMX Operator, you can create single-step scenes, then use that to build chases. You can then have the DMX Operator's sound to chase function to trigger your scenes. You can also control the time it takes to get from scene to scene, which can slow your Comscans down. The upside is you get a sound-active type effect, but with the speed you want within reasonable range. It's hard to dial in the time exactly, but you should be able to get sufficient results rather easily.
Now, if you turn sound active OFF, then of course the scanners are not going to scan unless 1 of 2 things happen:
1: If these support some sort of internal pre-programmed(or user programmable) pattern being run, they can work without the assistance of control. Chances are, in a master/slave situation, assigning one as a master should quickly and easily give you a show. If you have pan and/or tilt reverse options, that gives you more to work with.
2: DMX control via software or hardware, allowing you to have control over your fixtures as you see fit.
I do have many sound active fixtures. For example, I have many high-tech FX(all ADJ), and it really depends what is what. My scanner-type fixtures(Electra, Rover, Barrel Flex, Reflex) all move at what I consider smooth but medium speeds. These work fine for me and I have no issues or complaints. My other sound active fixtures are the Mystic, Vertigo, Trilogy and Double Twist, and since these are not moving-type lights, the sound active that they do perform is more than adequate for my needs. On the "higher" end of things, I still don't have anything like a ComScan, but I do have the 64 LED Pro, Mega Bar 50 and Mega Panel units, soon to be joined with more ADJ and Elation LED fixtures. Of what I have now, they all support sound active via DMX, as well as having a sensitivity selection. For how I use them, again, I've got no complaints. Between the macro scrolling and sound active funtions, I get a lot of instant color craziness quickly and easily. My Chauvet fixtures(DMX 500 and Q-Spot 150) both also support sound active modes, but both also have speed control adjustments. I like the DMX500's color wheel spin function(that's all I get in sound active), and the Q-Spot's random movement that I can couple with controlled color wheel spinning.
Personally speaking, in the direction I'm moving these days with software control and the ability to program, coupled with the types of shows I do, I don't really want an instant show type of unit.
I think your ComScans are working properly, especially since you state a friend has the same issue. I think it may be time to get yourself into a controller environment.