Hi,
You may be able to increase your buffers to take some burden off your CPU but if your HDD has slow RPM then you'll get some artifacts or chatter in your playback. Make sure you're using ASIO driver - and not the Magix ASIO. That uses less CPU cycles than raw wav.
Are you unable to add more memory? That is THE fix and is not very expensive. Realistically that is probably the only way to fix your problem.