It's difficult to get homemade CDs as loud as the ones you get in the stores, because they compress the bejezzus out of them. Get about $10,000 worth of compression equipment, and a 10-year or more experienced engineer, and you'll have it. Otherwise, compress the dynamics out of your mix, then run it through something like Audacity to boost it even more. Just remember if you boost digital too much, it distorts horribly.