Macpro early 2009 osx El capitan having audio problems

LS, white running Reason 8.3 with a few audiotracks de sound starts distorting. When running Logic pro it gives systeem overload. I.m running a macpro 4.1 early 2009 with 2x quadcore Intel Xeon 2.26 GHz. And 20 GB Ram. Someone out there, who knows what's going on?

Greetings

Gert