IF you are running gain at 75% then I highly suggest trying a preamp. These mics have a pretty hot output. Any chance you have pads and or rolloff or eq engaged on the fostex unit? I used one of those for a short time and was not really impressed with it and actually returned it. If anything I found the A51s mics to have a little TOO MUCH low end response. So really odd you think that they are lacking there