I can answer your question 2 ways. 1st, yes an amp will improve not only the bass but the overrall sound of your 40s. Generally, the amplification is the weakest aspect of most receivers, and their ratings are often based on a narrow frequency range driving 1 channel. Not 2 or much less 5 simultaneously. I have an Arcam AVR100 with Maggies, and was amazed at how better my bass response was when I added an Ayre V-3 amp. The Arcam is no slouch, but it has an almost nostalgic sound that can be a touch soft. The Ayre drives the speakers with more bass, dynamics and slam.
A 2 channel amp would also allow you the option of adding a 2 channel preamp for music later on. And just using the 3805 for movies, and to drive your center and surrounds.
2nd, the 40s are good speakers, and like most monitors don't have a great deal of bass anyway. If you stepped up to the 60s you'd be surprised at how much more bass you get. Whatever way you go, I'd get an amp 1st to better drive the mains, then decide later on if you need to look at changing out your speakers or the Denon.
I'm not sure of your price range, but an NAD 218, Rotel 1080, or perhaps a Parasound A23 is where I'd start.
A 2 channel amp would also allow you the option of adding a 2 channel preamp for music later on. And just using the 3805 for movies, and to drive your center and surrounds.
2nd, the 40s are good speakers, and like most monitors don't have a great deal of bass anyway. If you stepped up to the 60s you'd be surprised at how much more bass you get. Whatever way you go, I'd get an amp 1st to better drive the mains, then decide later on if you need to look at changing out your speakers or the Denon.
I'm not sure of your price range, but an NAD 218, Rotel 1080, or perhaps a Parasound A23 is where I'd start.