Tony gave a great response of what can be done. Just to add, for demo recordings, I wouldn't count on too big improvement @ high costs. If you have the chance, add some dry kick & snare samples with Drumagog or something and adjust the triggering with that drum audio file (if possible). This will help the drums to be more defined. The rest can be tucked in the overall mix in a more comfortable way. Record everything else dry, except one guitar or vocal, and don't overdo there as well.
Or if it is not a problem, get some curtains on walls, and call the drummer once again.