Bleeding blood or bleeding money? It sounded like a little (lot?) of both. I just get a kick out of how you tell your story. I would have thought you could have got those 37000 holes in that tube if you really wanted to:-)

I have never looked in a M200 since I don't have one, but I would think it would not take much to follow the trace from the input. My guess is it is the first component that the input connects to.

As that one link above to hometheaterhifi stated at the roll off is where you have the phase shift, so if you move the cutoff point down, the frequency where you have phase shift would also be moved down.

The impedance of a cap at a frequency f is Xc = 1/(2*pi*f*c). At the 3dB down point the impendance of the cap is equal to the input impedance of the amp itself. The M200 has a stated input impedance of >10K ohms. So at 5Hz that would give a cap of about 3uF, my guess is there might be a 2.2uF cap on the input. Switching the cap to a 4.7uF should cut the 3dB down point in half.

I could be all wrong here too. I am guessing without seeing a schematic or looking in a unit. If there is a cap, and you know for sure that your preamp has no (zero, nothing, nada) DC offset, then in theory you should be able to replace the "cap" with a wire. But don't hold me to that:-)

And anyone out there that is a bigger EE than me, you do not need to go off on me.