You've gotten lots of answers that I haven't read (due to having precocious kids myself :) haha), so maybe I'm reiterating something, but I just wanted to let you know what has worked for us.
I'm also a big nap-fan. We are very strict with our kids' sleep habits because I know how cranky they can get without the right amount of sleep; but I also know that the more used to a routine they are, the better they can slip back into the routine if we have events or whatever.
We kept my almost-8-yr old napping through kindergarten. We made sure that he got into a morning program so that he could go home and nap before heading to daycare (since I was working FT at the time, my MIL had to do the lunch/naptime). We finally phased out his nap during the summer before 1st grade. Was he probably the only kid his age in the school napping? Probably...but I don't care! He was such an ogre without it until he was more capable of managing without the nap. I did what was best for my child's napping needs. When he entered 1st grade, he was done napping and I became a SAHM after the birth of my second child. Now, my almost-2-yr old naps once a day for approx 2 hrs and I make sure she goes down at 1pm so that she'll be up--often by me waking her up--at 3pm to go get her brother from school. I intend to continue this pattern also through kindergarten for her. Also, whether or not she's showing overly sleepy signs, we get her to bed between 7-7:30pm. We did the same with my son when he was younger. I don't care if she's up there playing in her bed for half an hour as long as she's in bed. She knows what she's supposed to do and there's a better chance of her falling asleep if she's in bed than if she's hanging out with us downstairs.
So, given all of that, here are my thoughts on some things you might try:
Given the amount that he is sleeping total, I sincerely doubt that he's ready to give up his nap. Sleep helps their little brains develop...so I say, let 'em get as much as possible! :)
Are you making sure that your 2-yr old is going down for a nap at just about the same time every day? Since he sleeps so long, you might try getting him down around 12:30 so that he's up by about 3-3:30pm and then he's got almost 4 hrs to burn off his energy before bedtime.
Since he sleeps so late in the morning, if you make sure he's in bed by 7:30, he'll wake up at a more kid-appropriate time like 7 or 7:30am. This would be ideal for a morning preschool program that would then allow for the afternoon nap to happen, too.
If you're able to implement both of these changes, he'll be up earlier in the morning so that he'll be tired earlier for his afternoon nap, which means he'll be up earlier from his afternoon nap, making an earlier bedtime a distinct possibility.
Good luck to you!