In my test the PowerLeap bios can't free up IRQ 9, even you disable ACPI in bios.
According tyuper's post, some bios setting the SMBHSTCFG register to use IRQ 9.
I have check PowerLeap bios chipset register setting and confirm they do that setting.
I modify that register setting from IRQ 9 to default SMI# value, now the PowerLeap bios can be truly free up IRQ 9 for MPU-401.
The UpgradeWare bios keep SMBHSTCFG register as default but hidden "ACPI function" in Power Management Setup page; I also modify UpgradeWare bios to unhide that option.
By now both version of bios can be free up IRQ 9.
File base on gerwin upload bios in here.
Base on 4)upgware.bin to unhide "ACPI function" in Power Management Setup page.
Base on 6)powleap2.bin to change chipset register 3bd2 from 100 to 000 for free up IRQ 9.
In my test PowerLeap bios seems support LBA 48bit, it can be report 4TB hdd size correctly.