It seems that I need to find out more about the IRQ assigning policies... AFAIK this thing can only be settled by manually moving the card from one slot to another (but I only have two). Doing BIOS tweaking don't seem to be a good way to get it work... I don't know whether there can be a workaround to make the ES1938 to use IRQ 7 for DOS support... Its TDMA is always proven to be a reliable thing and can be used on any motherboards of any era, and in TDMA it consumes little memory (About 1.2K base memory, it will not consume any base memory if the board supports DDMA).
Actually the same thing happened when I tried to use YMF744B on my old Socket 462 board (It can be very tough to find motherboards with chipsets supporting DDMA) due to the same problem - it only allows IRQ5 of INTA (Actually I really don't know what INTA actually is, and it doesn't seem possible to move it to IRQ 7 which I always used several years ago), and somehow, it was once again the network card occupied the IRQ 5, rendered the IRQ unusable and thus will crash if it tries to play digitized sound.
Maybe for that I still have to search for better workarounds...
BTW, it seems this nForce4-based motherboard has a flaw with its PS/2 ports, which may fail, and thus the PS/2 ports aren't properly detected by OSx86... Problems that Keyboard/Mouse being unresponsive sometimes never happen if I use a USB mouse or keyboard.