Well, there is another manufacturer by the name of Adlink Technology Inc. but Magma was at least specified for audio. Looking at all possible vendors, it appears the technology itself (pci chassis expansion) is expensive.
Why not get another MOTU FW interface like the Traveller or Ultralite? It might be cheaper in the long run, doesn't bind you to outgoing technology like pci and it is 'portable' across OSX and XP/Vista.