You can use both together if necessary. I would start using both, and then when you see improvement, then try decreasing the Rimadyl. Hopefully with a little time then you would be using only a small amount of the drug that can have serious side effects. Often times, there are bad days (such as rain or cold) that cause increased pain, and so on those days you could give a little more Rimadyl. On the good days it would not be necessary.
Promaxol is very flexible because you can split the dose, giving quarter doses up to four times daily for a larger response, or you can also double the dose if the need arises. Some dogs do well on Rimadyl and others do not, so you might want to Google it to decide if this is the best NSAID in your case.
I also think supplementation is beneficial: Digestive enzymes, MSM, probiotics, vitamin C, and fish oil. Give only filtered water for drinking. All of the good things do make a difference. Please let us know how you do.