My head unit is a JVC KD-SH99. So far I've noticed about a 1 second delay in pressing a button before it will trigger on the head unit, so it doesn't work as fast as it did with the factory unit but it does work.
The delay arises from the infrared communication with the unit. I would think that there is a way to direct wire the steering wheel controls to the head unit.
Otherwise, there are a few head units out there that come with steering wheel controls (You'll just have a more cluttered steering wheel). For $70.00, it's probably worth being able to utilize the existing controls.
Installed it myself, I made a fiberglass piece that covers the hole but the left side of it broke so I have to make another one when I get a chance, also depending if I add an in-dash DVD player. It was my first fiberglass project so it looks so-so.
I have the JVC 12 disc changer also, mounted it under the driver's seat.
Do you have navigation too? If so, what'd your installer use to keep the voice?