40s and 60s are essentially the same speaker - identical drivers, just floorstander vs bookshelf (with differently tuned cabinets). I recommend as much power as you can afford for these guys, but that does not mean it won't work at all.
You could get away with the 1803 for a while, but I would definitely upgrade it in the future, especially if you go for a matching 470 center. Just don't crank it up to extreme levels, and it should be OK.
For six months I used a Yamaha 630 receiver to drive my Studio's 20... it was not bad at all, since these are amazing speakers... when i bought the Marantz PM 7000, an entry level integrated amplifier... the sound I got had NOTHING to do with the old one. These speakers deserve much better amplification than this Denon, otherwise you will be far from exploring the full performance they can offer.