You will be surprised at how much a powered sub will help. Not only will it fill in the low end, it will alleviate a lot of stress on the receiver which should make it sound better and run cooler at high volumes. Even a $110 10" Yamaha will do the job.
Also, consider just getting a 5 channel amp first if your budget is tight. The Denon should have 5.1 outs. Start with a nice amp and once budget allows, get the Anthem pre?
Also, consider just getting a 5 channel amp first if your budget is tight. The Denon should have 5.1 outs. Start with a nice amp and once budget allows, get the Anthem pre?