I'm still waiting for a response by SM. I asked if there is a firmware 20.00.04 with a newer NVDATA for the AOC-2308L-L8E (the SATA drive performance problem is a showstopper, if it also exist with the add-on card).
As far as I understand, there should be no difference in the firmware, regardless of onboard or add-on card. Of course, the controller should be the right one (in Jailer's and my case the 2308). But I don't wanna add any extra chance of damaging sth. Will report back as soon, as I have a response from SM. Till then, I will hold back "my" version of the firmware...