I finished my Crack and couldn't be happier. I made several personalizations. I also completed my Crack headphones but will post about that project in a different thread. I did implement the hum pot. This thing is dead quiet, even during power up. It is eerie the way the music slowly comes on if I power it up while playing something. Here is a list of my minor mods:
Replaced the 220uF caps in the power supply with 470uF Nischicon caps. (see another thread).
Replaced the Xicon power resistors with Mills non-magnetic wire wound resistors.
Installed a 100K Goldpoint switched attenuator.
Added a 220 ohm wire wound multi turn POT across the heater winding
Replaced the output electrolytic capacitors with MKP Film caps.
Used STP for input wiring.
Moved one ground wire.
Everything else is stock. This thing sounds awesome. Here are some pics. Thanks Bottlehead. Now All I need is a BH DAC!