I'm curious as to the frequency range of the 2 gauges, primarily because I'm considering adding a graphic equaliser in order to calm any nasty high frequency garbage.

Not as good as a stereo machine from uher would be for the same outlay at that time. Its about 8k - 10k at best, much of your eq would not come into play Stuart, and anything placed into the chain would add distortion to the sound anyway, and you would forever messing with the setting's I found. Unless you have one already or could borrow one to see the difference not worth it, you need one that has a bypass switch on to do a before and after test, I believe you will be fighting your 3 second memory mate.....

On occasions when I could be bothered to put up a full set up to watch a film, I found my 32 band Behringer equalizer quite useful for filtering out any annoying and completely unwanted frequencies but I didn't bother attempting to tailor the frequencies for each and every film.

I just set it once to the above best known general settings for all films on any given machine and then used the projectors separate bass and treble controls to adjust the overall tone and on occasions adjusted the tone further with a similar facility on an external mixer.

I use a power amp with zero tone control for the final output to the loudspeakers.

I do this now less and less frequently.

I have no permanent set up facilities so overall, I find it too much hassle putting it all up and down again for my needs.

I still on occasions connect two ext speakers and use the pj's bass and treble tone controls and generally find this ample for my own enjoyment these days.

If I had a separate and permanent cinema room, I would however use an equalizer in circuit permanently like the previous owner of my machine did.
His set up was very very professional indeed and he eventually outputted through to a pair of Craven loudspeakers in his air conditioned auditorium.