Hey Jason. Thanks very much for your comment on my post below. I mainly write this blog just for my own amusement and to show the occasional friend what I'm up to. Sometimes I do wonder if anyone else has ever actually looked at it. ;)
You raise a few interesting points I'd like to comment on so I'll just point them out, otherwise this'll turn into another massive rant:
Nine layers? Wow, well you're braver then me! :) I did at first consider doing something different, like a sphere or pyramid, but the more I looked into it, the more I realized there are some pretty good reasons why the 8 cube is so popular. Maybe most significantly eight is a "byte" and a power of 2. So is 64 and so is 512. Having 8 layers to multiplex, and 8 "blades" becomes extremely convenient when you start mucking around with the data. There's 12 TLC chips, there's 12 bits per channel, there's 16 channels per chip, there's 16 bits per SPI send, they all divide nicely into each other. A central axis does indeed sound great, but an odd number of LEDs means you'll constantly have an odd "left over" bit (or bits) to deal with.. Don't mean to scare you, I'm sure there are probably ways to deal with this, maybe without too much trouble, but it was more then I thought I'd be able to tackle.
Sometimes when I'm feeling a bit bummed out about my project, it occurs to me that If I had started a 4x4x4 RGB cube, it would almost certainly be finished by now. There will definitely be highs AND lows, so don't let that discourage you.
Multiple microcontrollers are also probably not impossible, but as you note it adds a whole layer of complexity. If you can sort out the synching issue, it might actually not be that big a deal, but you'd need to invest a bit of time just to find out. It might just be a matter of synching everything to an external clock. The slaves can "draw" the cube fast as they can, but it doesn't mean the "animations" have to be that fast. I actually think it makes more sense to keep the animations at 24-30fps or so, even if you can get your cube refresh up to 60hz - 100hz. I'm yet to decide how far I'm going to try to push the pic32.
As for moving to PIC, you might not have to! I also started my very 1st single color cube on an AVR. Back when I started the 8x8x8 project tho, there was no AVR chip that competed with the mid and higher end PICs. They had actually announced the xmega, but, let's just say, "good luck getting your hands on one of those" back then. However! That was a year go, and having a quick look at sites like http://www.evilmadscientist.com/article.php/xmega seems like they are around now! So, that's definitely an option for you. It'll be a little bit of a move from arduino, but not "that" much, I ported the acleone arduino TLC code to "straight" AVR without too much trouble, easier then to PIC that's for sure. (If you haven't seen that code yet by the way, you must have a look at it http://code.google.com/p/tlc5940arduino/ I found it a massive help and I wasn't even using arduino) Also, the avrfreaks support forum is awesome! I mean really awesome! Compared to the microchip forum.. No offence to the people on the PIC forums, I've talked to and got help from some amazing people on the PIC forums, but the format is just not as friendly for someone like me; it's quite technical, broken up into a hundred sections, fairly "formal" which is probably great for people who actually work with PICs. But the AVR forums are just amazing, more informal, only a few main sections, very "hackish", very involved, people have a great sense of humor, that's definitely the thing I miss the most about leaving AVR… Far out, reminding myself about this makes me think I probably should have looked into xmega again, before jumping into pic32! Oh well. ;)
Another thing i came across which convinced me I needed more processor power was this site http://lumisense.com/?page=eightcubed you might have seen it. For their "version 2" they actually use an intel ATOM processor, which is essentially a PC, running linux. Don't ask me how they actually interface the cube, i have no idea. :)
Cheers for the link to your site, http://www.photosbyjasonsmith.com I'll definitely keep my eye on it. Good luck with the soldering, I still remember the relief I felt when I got to the end! Put some music on while you're doing it, that really helped me through, and re-runs of Futurama. :)