If Avanade straight up purchased softnet with the intention of keeping them private, they'd have to offer a buyout of all outstanding shares. There would be an audit of all financials, assets, and current business relationship values. From there they'd negotiate a fair market value of the company, and then place an offer based upon that for the shares. That value would most certain be MUCH higher than the current PPS.
However, if Avanade were to do a reverse merger into softnet there's more to gain IMO. They could merge into this corporate entity, do a symbol change, and gain a much larger capital base for growth. There would be some other things that would most likely happen if this were to occur. Check out this post for some ideas and details.