Hey,
thanks for the hint! I didn't know that the MKM-003-00 is renamed in the custom fw so that the write strategy is messed up for that media. I corrected the name in the cfw, reflashed the fw and enabled 'Force HyperTuning' and 'Online HyperTuning'. The result is 6x burning with pretty good quality:
Model : 4-0-0-0 J:ATAPI iHAS124 B AL0S
Disc : DVD+R DL , MKM003 [Mitsubishi Chemical Corporation]
Scanned range : 0 - 3827484
Sampling count : 224963
Errors : 0
PI Max : 40
PI Average : 0,63
PI Total : 17623
PIF Max : 4
PIF Average : 0,05
PIF Total : 1525
Keep up the good work! :-)