For me, at least, the "best" PCI sound cards are the Yamaha YMF724/744/754 cards (at least a few of them, not all, since some were built cheaper than others). These are actually my favorite sound cards, period! I find them better than anything else, even better than the best ISA sound cards. All of them have authentic OPL3 sound and are extremely compatible, even when using the ddma emulation: dsdma (which is what you will need for the Intel 815 chipset). Please note that DSDMA requires expanded memory, so a few games that don't work with expanded memory will, of course, be unplayable (well, unplayable with sound, anyway 😀 ). Also, If you find a good manufacturer, the card will also be extremely quiet, much quieter than 99% of ISA sound cards that have OPL3.
DISCLAIMER: This is my own personal opinion, what works for me might not work for somebody else 😀 "Best" is a relative term.
Now, the big issue for you will be the CPU, which doesn't offer much flexibility. It basically has two states: extremely fast (with the L1 cache activated) or extremely slow (~386 speed with L1 cache disabled).
Your video card is also not exactly suitable for DOS gaming...
Bottom line, if your plan is specifically DOS gaming, you should go with either a Pentium MMX or a K6-2/3+ PC. Pair them with a Riva TNT, Voodoo Banshee, or even an S3 Virge DX and you're good to go.
2 x PLCC-68 / 4 x PGA132 / 5 x Skt 3 / 1 x Skt 4 / 9 x Skt 7 / 12 x SS7 / 1 x Skt 8 / 14 x Slot 1 / 6 x Slot A
5 x Skt 370 / 8 x Skt A / 2 x Skt 478 / 2 x Skt 754 / 3 x Skt 939 / 7 x LGA775 / 1 x LGA1155
Current PC: Ryzen 7 9800X3D
Backup: Ryzen 7 5800X3D