The cheapest option is to render WAV/CUE or burn a CD in Wavelab 6 and find a program to make DDP from that. But I don’t think it’s worth the hassle when you can get an upgrade to WL9 for a reasonable price.
I don’t think you’d find anything missing. And a lot added. I think video was dropped but that’s all I can think of.
The upgrade price I saw on the link in my post was $250. x 2 for two copies $500.
Or like I said you can render WAV/CUE image in WL6, from which you can make the DDP in Sonoris and probably Hofa. Or I think there’s even a free command line DDP converter if you do a Google search for CUE to DDP, but I have no idea how reliable something like that would be for plant acceptance. But it might be fine. I would do some checking first.