WHAT THE HELL!!!
I was always under the impression that you couldn`t split the A4000`s IDE interface because it was 'buffered' whereas you could split the one in the A1200 because it isn't buffered.
Read it in some Eyetech notices/webpages back in the day...
Eyetech were technically incompetent. They knew nothing of the HW they sold pretty much. Most of them were rebadged products from 3rd parties anyway.
Whether the interface is buffered or not is irrelevant really. Don't get fooled to pay more for simple IDE-splitter just because it's "buffered". Practically there's no difference to non-buffered one.