Trying to set the metronome volume on all beats to the same does not work. I have the audio metronome set as default and I have all beat options set to the same volume and the downbeat is always more present. Same beat sounds, same volume set to -3. using the metronome that way always plays the downbeat louder during record and playback.
 
Would you not expect that these beats being set to the same sound would result in even loudness?

Just wondering...why would you not want an emphasis on the downbeat?

because my bass player has bipolar attributes with ADHD and the uneven sounds attracts his attention more than it should. :) He asked me to do it. I am fine with different sounds.
 
With that said,. I use a Yamaha metronome while giving guitar lessons that has  the ability to flash a LED with the sound. The metronome audio and visual cues do not emphasize the downbeat with that unit.