You're feeding a passive DI box designed for line levels =~1V with an instrument signal much lower. Some kind of preamp would be useful, maybe your GT2 would get the levels up. Either of your multi effects would handle it but you'd need to use the headphone output on the ME50 or crank the output level on the Digitech if you use those. Plugging into a high impedance input just gets you into problems of signal loss unless you're using short cables.