I've got an 135W adaptor on order that I can try tomorrow. I'm interested to get to the bottom of the problem as it seems like there are a few people who have odd compatibility issues.Sounds a little like the problem at the top of this page, which didn't get a resolution. I would suggest the usual things, update firmwares etc, and then I would look at temperatures if you can and make sure you're not shorting something somewhere. The slot itself is only 8x, irrespective of the riser.
A 65W power supply may be the issue. It's not super efficient, so you're perhaps only getting 55W in reality; plus the processor is not really capped at 35W, it will use more if it can. So 5-10W on your card and 5-10W in storage, motherboard etc and it's possible the power is insufficient. Finally, might be worth resetting the BIOS to defaults and then setting it up again, you never know.
Annoyingly aside from another almost identical LSI HBA I don't have any 8x adapters to try. Out of curiousity I tried an ancient ASUS 4x wifi adapter which worked okay.
I'm interested to know if its a limitation with cards with their own BIOS. I'd expect to see the LSI bios at some point if the card was booting correctly.
I suppose another solution would be to use a more simple 4 port sata card, and fashion a SATA external caddy, rather than SAS.