Now that I know the best solution I'll take up the OSB and put down 3/4" plywood fastened with 3" spiral nails. Thank you for your prompt response.
Based on what I've read from others who put hardwood on any thickness OSB or had a new house with hardwood floors over OSB, you are just asking for trouble. One person (on this site or another one) moved into a custom built house with hardwood floors placed over OSB. A few months later (not even years) the floor was squeaking.
One last question, I discovered that there are different grades of plywood. Should I go with BC or is CDX okay?