Since a Thru output is simply a parallel of the In, any load connected to a Thru is placed in parallel with the input load of the DI device itself. No way around that. A potential solution is for the DI device to switch to a much higher input impedance when something is plugged into the Thru jack.AND thru
Part of my reason for recommending output level controls for both the 1/4" and XLR output.it would be awesome if the line level didn't drop