Volume control for power amp

Hi and thanks for reading this post.

I have a 3-way active set up at the moment with one amp driving the tweeters, another amp driving the bass units and a quad 405-3 power amp driving the mids.

The problem is that there is too much midrange information coming through the speakers and with the quad being a power amp only there is no volume control to adjust the sensitviity.

I am thinking of soldering a resistor across the positive and negative terminals of the phono input (screened cable) of the quad in an attempt to lower the volume a little.

Do you think this is a good idea, if so what value resistor should i use.

Many thanks in advance. John.