When you say you want more juice, does that mean that, with the volume turned all the way up, you don't have enough volume? The .4mv output and 60 db of gain from the Manley should work, even if that means cranking the volume knob up more than with the AIda. There is nothing wrong, by the way, operating near the top of the volume control range; that is actually where volume controls work the best (they sound better and have more even channel balance). Do you know if the linestage this feeds into has gain too? If you really need more gain, that would mean using a step up transformer and feeding the output to the moving magnet input of the Manley.
If by more juice you mean the cartridge doesn't sound as lively, and you are not necessarily talking about ultimate volume level, that is a different issue. It might well be the case that the Koetsu just sounds a little mellow by its nature. To some extent, the sound can be changed by changing load, by changing the setup (change in VTA/SRA particularly) or by trying different tubes in the Manley.
If by more juice you mean the cartridge doesn't sound as lively, and you are not necessarily talking about ultimate volume level, that is a different issue. It might well be the case that the Koetsu just sounds a little mellow by its nature. To some extent, the sound can be changed by changing load, by changing the setup (change in VTA/SRA particularly) or by trying different tubes in the Manley.