PCI soundcards can be tricky in DOS, depending on the drivers and setup options. I do not have much experience with the soundcards you've mentioned since I mosly stick with ISA cards in DOS.

The SB live seems to do pretty well in DOS:
https://www.philscomputerlab.com/sound-blaster-live.html

undoubtedly you'll run into problems but it might kinda work if you don't have resource conflicts. I'm not sure if those can be solved.

One problem about the live/audigy vxd drivers is they dont allow you to manually change resources in the device manager.

The XG VXDs do but I don't think the XG is better than the live unless you have PCI/PCI as there are a lot of problems with the driver implementation without PCI/PCI or DDMA it doesn't work right in dos box with some games like duke 3d and tyrian for example.

XG is good I guess in pure dos becasue the TSR lets you use OPL3 in dos but no midi.

I've had a similar setup in the past.
Win98 will work happily with 2 sound cards just set the card you want to use as the primary device.
Dos I had 2 "exit to dos" shortcuts on my desktop, one for the Creative and other for the Yamaha.

I seem to remember the Creative drivers were fighting something and it was just easier to have 2 configurations and reboot then work out how to get everyone to play nice.

generally the midi works really well on the XG windows dos box with VXDs without pci/pci its the opl part that some games don't like becasue some games hang or crash when you try to configure OPL from XG

Not every game likes the live drivers either..