I learned some thing today that is good and bad. From information I found at http://www.madronalabs.com/DIY it seems my original guess that only 100 samples per second on the touch-pad would be adequate for a music pad seems to be incorrect. Randy demonstrates a system that he claims requires about 1000 samples per second or a bit more. The good news is that he seemed to get the X and Y axis resolution from only 8 channels of A2D to make a surface of about 8 X 8 inches to work. So what this means is that the Synaptics 7300 asic chip will probably not have a fast enough sample rate to work in this project. I've also sent a letter to Sensibleui.com in hopes that there sample rate might be fast enough and at a price within the planed budget of less than $100 per unit. I had originaly thought 200hz sample rate was good but when I saw that the synaptics 7300 chip could only sample at 100hz I thought that would have to do. Also the Madronalabs Soundplane instrument is exactly what I had hoped to create with off the shelf parts. There Soundplane unit IS for sale NOW but at a price of about $1800USD. Way above my budget. They also explain that the parts used in the Soundplane instrument seen on his website and on youtube.com are not off the shelf that they were made in house. The video is also fantastic showing just what can be done with a pressure sensitive plane device. The size and shape and everything about it to me is perfection.
Update with a return from Randy at Madronalabs.com:
"100 Hz is way better than 0! In other words, I think there is a lot of fun to be had and a lot to learn, without meeting any particular goals for sample rate.
Thanks for writing and I look forward to seeing what your exploration brings".
So at least he provides us with continued hope of some success.