First problem I see is too much memory!
Remove 512meg ram, windows 98 starts to misbehave with out of memory errors and other weird issues if you have more than 512meg memory installed. There might be workarounds for these problems, to allow more memory to work, but my recommendation is to start with only 512meg ram, at least while you are trying to work out your system.
Then you can install the vogan drivers package I linked about and have the DOS drivers load in config.sys and autoexec.bat before windows starts (typically these are fine to load before windows 98 starts)
One other thing, which I think won't be a problem for you, is that I also know that I wasn't able to get my audigy to work in DOS on my pentium 4 system with Intel chipset. Just not supported. But works fine on my SIS Pentium 4 motherboard. So motherboard choice can be a big issue, especially as you get into the faster P4 systems.