Well I had to play around with RAM a lot too to find a set that works fully. The DKB seem to be quite picky.
I made one discovery during my tests back then: I had a set that was only recognised as 64 MB, but when I replaced the last 32MB module by an 16 MB one I got at least the 112 MB that I should have. As I said I had to search quite a while to find a set that adds up to 128 MB, but maybe you can live with "just" 112 MB on the DKB.
