Hi there Chris
I would think that owning Pro Audio 9.0 would qualify for the upgrade price. However, if you haven't already done so, you might need to register it before you purchase Guitar Tracks Pro 4.
I see the regular price for GTPro4 is listed as $139, but as you can see here, the upgrade price for registered Cakewalk users is just $79. That's a great saving and makes GTPro4 a bargain in my opinion.
If you don't have an account with Cakewalk, you'll have to create one and then register Pro Audio afterwards. It only takes a few moments, click on
THIS LINK to go straight to the New Users page.
So I'd suggest you make sure your copy of Pro Audio is regsitered and then just check the upper option in the Upgrade Selection window and see if the reduced price is successfully applied.
You'll be able to see if the discount has been applied before you part with any money. If there is any problem with the upgrade price not being applied, you will probably have to get in touch with Cakewalk's Customer Service - click
HERE to view the details.
Hope that helps!
Steve