Digidesign's 003 top LE product can record simultaneously 18 input channels.
Is there a way to connect two units in order to have more inputs or is 18 the highest you can get?

18 is the most you'll get simulatneously. That is only with another a/d that has adat optical outputs and if you want that extra 2 inputs you'll also need another with spidf outputs or an a/d with more than 8 ins and outs and optical and spidf outputs. You will probably want to keep from spanning anything that needs to be phase coherent across the analog, optical or spidf inputs. Everything should be clocked off the same source or you'll run into problems.

http://www.dolphinmusic.co.uk/shop_image/p...772ab720bdb.jpg


This will give you another 8 inputs via adat. I have a 002rack and always thought it would have been nice to daisy chain these units. But alas no...