Gotcha. Was there anything plugged into the headphone jack of the MJ2 (including something like a 3.5 to 6.3mm adaptor)? If anything is plugged into any of the hp jacks on the MJ2 it will automatically send the signal to the headphone jack and not the pre-outs in the back of the MJ2. Very few commercial hp amps pass the signal to the headphone jack(s) and pre-outs simultaneously. Other than that just run the pre-out on the MJ2 to the input of the LP and you should be good to go. Run your source to the input of the MJ2. Hope this helps.