... I find the bass on FM much too loud, so I will quite happily alpha test. Is your patch a complete
vol adjust per source
When it is a patch

.
, or does it have different Bass/Treb/Vol settings for AUX/DSP/AM/FM?
Sorry no. Tone and Volboost are 2 separate features.
If anyone wants to decode the following, then it'd be relatively easy to decrease the FM bass boost:
/* Load bank1 with bass boost:
Values calculated by cdsp.exe
+6db bass, 0db treble, first order cutoff 125Hz */
dsp_write(Y_Ctl1,0x055);
dsp_write(Y_Cth1,0x3ee);
dsp_write(Y_Btl1,0x000);
dsp_write(Y_Bth1,0x000);
dsp_write(Y_At01,0x008);
dsp_write(Y_At11,0x008);
dsp_write(Y_At21,0x000);
dsp_write(Y_KTrt1,0x4c4);
dsp_write(Y_KTft1,0x662);
dsp_write(Y_KTmid1,0x402);
dsp_write(Y_KTbas1,0x47a);
dsp_write(Y_KTtre1,0x000);