Will there be any performance penalty with these workarounds ?
"but I also think about a real fix on DENEB for enabling several busmasters on Buster 11 "
It's the only reason holding me from getting a Deneb. Though I think that if such an amount of logic is derived from Buster to Deneb maybe you could use that in some kind of multiple DMA enabled ZIII/PCI bridge. It would be the only one in the market (Mediator in NOT true DMA).