Six drives? Or do yu mean six parttions onone drive? Or some combinaton of drives and partitions?
Wubdws 10 wants to replace the boot loader used by older versions of Windows.
I have installed Windsows 10 a numbver of tmes just for the expoerince. I noticw taht some combinatons of drive partitions don't work.
You might consieder installin WIndows 10 on aspare hard drive. And let Windows 10 delete and format it. (But taht is not alwasy necesary.)
Also, when you boot the Windows 10 installer from aUSBdrive, avoid having anyother USB drives on the system. That even apploies to the HP promnter that has a USB drive when connected via USB. Drove me crazy!