I've sprayed acrylics over enamels with no problems, but be careful when spraying enamels over acrylics. I've seen paint curdle, crack, and peel.
Dullcote is ok over acrylics if you allow it time to cure, usually 24-48 hours. Apply it in thin coats instead a heavy one.
I now use acrylics for just about everything, and have given up on Dullcote. I now use Future mixed with Tamiya X-21 Flat base. Swanny (the Future Guru) did an article in this month's FSM, including mixing ratios.
Jeff Herne