The only thing I tried was the ASUS tool, since the DD-WRT list of supported routers says only: "Recommended: use ASUS Firmware Restoration Tool for ASUS router initial flash (*.TRX file)." When the recommended approach failed, I figured I should get more information before trying other things...
I picked up an Asus RT-ACRH13 router (which is compatible with DD-WRT) over the weekend, but I'm running into problems getting it to flash the initial factory-to-ddwrt.trx file using the recommended official Asus Firmware Rescue Tool.
I first did a hard reset (hold WPS while plugging it in...