That is is also my problem. I can't get the alt-key to work properly. I noticed that when i "press and hold the command key", this gets translated in to "rapid firing the alt key".
Instead of PlayonMac, you could try running the application in wineskin, since they use x11. While doing google searches on this topic, I noticed that Wineskin has a special menu setting, for fixing the alt-key problems. However, I have not tested this myself yet.
See this image of the "wineskin advanced menu", and the entry, "option key works as alt":