Thanks 1st of all!
Which ASUS BIOS version did you use?
The modded one complains "floppy disk fail" and hitting F1 reboots the machine.
Maybe the version you used doesn´t support the SMC chip?
I used this one:
t25i0207.zip
In the meantime I upgraded my FIC PT-2200, a HX board with AMI BIOS, with a second TAG chip:
pt2200_2_tag.JPG
There was one 128K chip present, these are hard to find, so I soldered 2 x 256K.
Then I activated the hidden BIOS menue entries with AMIBCP, activated 512MB enlarged cacheable area and - Bob´s your uncle.
The resistor that needs to be moved to switch from pulling TIO10 high to low is located between the chips.
So the PT-2200 is the first HX board I came acrooss to run fully featured HX L2 cache with AMI BIOS! (there´s also an AWARD BIOS available for this board that works also).
This is the latest BIOS version with all the switches enabled:
TII107_512.rar
Then I tried this AMI BIOS in the 54TPI and the enlarged cacheable area is activated without any problems.
BUT, there´s no SCSI and, even worse, the FIC has a rare National "PC87336VLJ" Super I/O so I have to use an ISA I/O card.