The best advice is that you need to retain an attorney right away, the consequences of another conviction and probation revocation are very serious. An attorney can get access to the evidence and start mounting a defense and potential plea and that needs to start immediately. Be careful discussing details of your son's case on these forums as well because prosecutors also read them. This is very stressful for the family and a mom, having someone fighting for you that can keep you and your son informed will help ease the stress " a little."
You need to hire an attorney for your son tomorrow or ASAP. He is looking at prison. Probation is a privilege and picking up another felony while on felony probation is going to cause any prosecutor to seek prison and most judges to grant it.
The information provided in this answer does not create an attorney-client relationship. If you are interested in his legal services, feel free to call Chris at (303) 409-7635 at his law office in the Denver Tech Center. All initial consultations are free of charge.