As far as I can tell it's an emulation issue, the game requires 2 MB (the MAME default is 4) and it should be playing ADPCM sounds even with that.

Runner's High supports the PC-9801-86 sound card, so you probably want to use it. Also, I'd recommend using a 486-based machine like the Ce2 for the best speed.

The "right" way to run it would be using the DiscStation 10 CD, but there's also a "fake" floppy version in the softlist that was ripped from the CD, and it's easier to use. You could use this command line:

mame pc9821ce2 -cbus0 pc9801_86 -flop1 dstat_10:flop2