I started with Pro Audio 9. I was heavy in to it. It wasn't on my PC so when I lost contact with my bud who had it, I lost contact with Sonar until we got back together some years later and he was on Sonar 4 at that point.
Some of the stuff we did with PA9 was very impressive. He had an AWE Gold card with the Sound Font daughter board add-on card IIRC. It was quite an impressive setup, especially when playing games. IRQ=7, DMA=1, Port=330. wow! now there's a flashback for you! :) He was really in to making his own soundfonts but I could never understand how it all went together.
I really liked working with someone who had the same musical ideas as I did and both of us knowing the software made it a lot of fun.
I have the cash to get my own gear and set up a small studio in my house until around Sonar 8PE. I've upgraded every time since then.