Hm, when I created the HammerheadFX Section, I stumbled across alot of undefined and 'fishy' Information...
It seems the classic Version of the HammerheadFX was the 15 pin Gameport Variant, but there seems to be later Versions with USB.
Technically, the HammerheadFX apparently evolved from SV-262A upto SV-262F (moving to USB at one point), but little to no Information is available on the Web

All Images found about the Hammerhead always show similar/identical Hardware, yet under slightly different name (FX, FX Pad, SV-262, SV-6565) and even varying description *arg*

The fact, that the official Product name/owner changed from 3dfx to Interact at one point in time doesn't quite help either.
Maybe Archive.org has some "original" Info's about it on one of the archived 3dfx.com Product Pages....