Sorry for the wall of text in advance.

So a while ago i bought the Custom Audio Electronics Line Driver/Boost and i run it through the effects loop of my JCM 2000 DSL 50 to use it as a footswitchable master volume. Its worked great for me so the other guitarist in my band got one for Christmas. He actually got the Boost/OD but its basically the same thing. He plays through a 100 watt Vintage Modern. So he tries doing the same thing I do with the pedal but he isnt getting even close to the volume i get. So today we tried to figure it out and are still lost. I tried his pedal through my amp and got a great volume boost. So the pedals fine. Then we thought the fact that his amp has one master volume and mine has seperate channel volumes might be the problem. So we tried it though his JCM 2000 TSL 100. Nothing. So im thinkin its not the amp. It was all hooked up right, we double checked. Other than power supply (both the 9V inputs on pedalboards) and the different wattages of the amp we couldnt come up with anything else to try and both of those would seem to be irrelevant. Any ideas? Thank.
so your friend has a Vintage Modern and a TSL? So you tried it on all 3 amps?

doesn't make any sense especially if the cables were all the same too. Did you move cable with the pedal when you switched amps?

power issue?

not sure man