I wouldn't really consider the analog gain trims to be a 'volume control'. They are used to trim the output level to match the output of the left and right channels for accurate stereo imaging and correct matching of the HEDD to the next device down the chain.
What you really need is a proper monitor level control between the HEDD output and your monitor input. A good quality passive attenuator would be the best choice.
Something like the NHT Pro
PVC - Passive Volume Control would do the job nicely, alternatively in the higher end something like the coleman audio
DAW monitor section is a good choice.
Cheers,
Marcus
PS do you reckon you could shorten your signature, IMHO it's offensively long and I dunno about that advertising, I assume you will do drum tracks for free ? If not I thought commercial advertising was not permitted here. Didn't some poor DAW builder get crucified over it ?