As you seem to be quite comfortable with modding you should have look at Aminet/Docs/
HardwareA few that stuck out were;
http://aminet.net/package/docs/hard/Maps1It contains info you should read before plugging in a Sega joypad.
http://aminet.net/package/docs/hard/S-Video_A1200Handy for connecting to LCD TVs and PC capture cards.
http://aminet.net/package/docs/hard/2HDsOn1200It shows you how to connect 2 ide devices using modded cables, this should apply to A600s as well, you have to keep cable lengths to a minimum though, the on board IDE interface is unbuffered.
Personally I'd recommend spending some money on a buffered 4 way splitter as it's safer and opens up a few more options.
A popular mod for A1200s at the moment is to fit a laptop drive indside the case, this can also be done with an A600.
Laptop to IDE adapters can be bought on ebay and take power from a floppy power connnector. They don't have a master/Slave jumper though and as far as I know they default to slave.
Another popular mod at the moment is to use Compact Flash cards as hard drives. You can buy single and dual bootable CF to 3.5 IDE adapter, they are powered from a floppy connector and have a Master/Slave jumper.
I recently added a 4GB card and a dual adapter to an A1200 for about £30 including postage.
