Hum is mostly a system issue as anyone component cannot be the cause.
I have been busy but do want to solve your issue and this may help others
so let me ask some simple questions
if the LAMPI dac is off and Hums do this and comment
if the dac is unplugged does your setup hum ?
If you change the input to an unused one does your system hum ?
have you tried a small gauge wire as a ground from tje ground post of the LAMPI to a ground post or screw of your preamp ?
answer these then we move on.
lastly keep any WiFi router or access points closer then 5 feet. Also unplug these and take note. Hum is mostly a simple ground loop and can always be cured but it does need to done with a method and note taking.
good luck and please let be help you.