You are welcome ... no problem.
I posted this at misc@ months ago.
http://marc.info/?l=openbsd-misc&m=145350181109130&w=2
I haven't tried the 6.0 kernel but 5.9 boots without problems in a installed system. My workaround was :
Install 5.7 from CD, configure network (in my case urtwn), download the 5.8 bsd.rd, run signify, overwrite the original in /, boot from bsd.rd, upgrade to 5.8, reboot and run sysmerge. Do the same for 5.9.
For dualboot have a look at the above link from jasper and rEFInd.