I have tried everything I can to get this PCIe 424 to show up in the ASUS Z-170 motherboard, including two PCIe cards and NOTHING..NADA..ZILCH. BIOS version is newest, it is a PCIe core system board and it doesn't show up.
 
THOSE with Z-170 MoBo's what interface do you use????? Should I dump the board????  Sheesh!

Just a silly question , have you checked for any conglfuguration options for the PCIE slots in your bios? I had a similar issue with my delta 1010 back in the day and there was a bios configuration that got it to to work.

I just built (2 months ago) a new Z170 system using an ASUS motherboard and an i7 6700K CPU.  The new motherboard only has PCIe slots (and only USB 3.0 ports on the rear I/O Panel).   I have three PCIe cards installed, two USB 2.0 port cards and a Firewire 400/800 card, they are all recognized and work properly.  I use the Firewire interface for my MOTU 896mk3 Hybrid.
 
Did the MOTU PCIe card work in an different PC?  Looking on the MOTU site, this card was released in 2006 which was the Win XP days and way before Z170 or even Z77 motherboards.
 

Ya, I didn't get it ranting about a audio card that is long past it's service life. 
You can't expect a company to waste resources on old outdated gear. Yes for a few years it is expected, but 11 years is unreasonable. 

I have the pci-e card working.  It's boss man.  I think settings in bios might be the culprit?