@ Fernando
Some updates. The ASMedia drivers that I used and had problems were the archived ones from station-drivers, inside the achive there are different executable instalataions for W10 and W7,W8 and I used the W10 executable setup which installed the ASSTAHCI64.SYS driver.
Inside the W10 driver folder there are also subfolders contaning various drivers for manual installation, one of them has an alternate ASSTOR64.SYS driver which I manually installed.
I have been running the ASSTOR64.SYS drivers for 5 hours and the only event errors I had, was 2 warnings for each of my 2 internal ports ("Reset to device, \Device\RaidPort1, was issued" & "The IO operation at logical block address 0x0 for Disk 5 (PDO name: \Device\00000037) was retried."). No more BSOD and I have back my port multiplier functionality.