Hi Midivox, I dumped on you in the other thread for not providing specifics but that doesn't mean I'm not willing to help out if I can. Now that we know what your using here's a few comments.
I completely agree with you about the manufacturers not being able to standardise a lot of this stuff. All I can say is musicians doing this kind of work are a tiny percentage of the PC world and nobody cares about us. It's up to us become total nerds to figure it all out and I was suffering through all this crap too several years ago.
As you've found out ASIO is tricky. Unless you're using a very recent system, you can't use ASIO in more than one program at a time. If you have RB open using ASIO and your other DAW, Magic whatever it is, they will conflict so you have to put one to WDM or MME as PG calls it. Your system has a lot to do with it too. My old P4 2.8 system never worked well with EMU's ASIO. I had to use ASIO4All and even that didn't work as well as it should. My new Athlon Phenom works great with EMU's ASIO. This goes back to your standardization comment. We just have to live with it.
I have the EMU 1820M and when I installed it it said in big bold letters "you must uninstall any Creative soundcard drivers before installing the EMU drivers". I know you've been using both for years but that doesn't mean everything is working properly. I would uninstall both the Creative card and the EMU card and then reinstall the EMU. I can't remember now but I think that after the EMU is installed you can then reinstall and use your Creative card. Check EMU's documentation about that.
You mentioned "With BB I have always just used the software midi instruments on the soundcard itself. In this the Creative Synth A and Synth B." Synth A and B are not considered software synths. They are hardware and you can't use them to render as Mac said.
You talked about never being able to use DXi synths. I don't know what the problem is because I've got a bunch of them including several DXi's I got from Cakewalk when I bought Project 5 and they all work fine in Biab and RB. Tell us exactly what synth doesn't load and what you did to try to install it because if you can install them then you can use them to do the fast render.
VST's are different. They work fine in both programs but there is a very specific way you have to install them. Once a VST synth is installed it will do the fast render as well. There is a tutorial about that but if you can't find it come back here we can explain it to you.

Bob

Biab/RB latest build, Win 11 Pro, Ryzen 5 5600 G, 512 Gig SSD, 16 Gigs Ram, Steinberg UR22 MkII, Roland Sonic Cell, Kurzweil PC3, Hammond SK1, Korg PA3XPro, Garritan JABB, Hypercanvas, Sampletank 3, more.