Problem with preamp volume control

Great that you have it solved.
To summarize my comments on the various options.
1. Al was spot on. hey. he's two for two in my book this week.
2. messing with cartridge loading (between cart and phono preamp) is dicey unless you redesign the interface as a system, and with full schematics.  Simple answer: if you have to ask, don't.3. You can often modify the line or amp gain - and its far less sensitive to various loads in those places. Sometimes even a setting.
4. You can successfully add an attenuator between a preamp and amp, but again need to know the I/O impedances first. IN fact nearly every amp has a voltage divider of sorts right at the front end.  Simple to just change its ratio.

Comment:  18 dB in a in the stage is a huge amount! I typically have 6!  and at most common knob settings, its fractional. Yikes!
G

ps: rare problem!  Most people don't have enough gain with low output 'coils. Tons of gain without noise or hum (which is a form of noise, ok, ok) is tough.  be happy you have it.

build build an in-line attenuator inside a m-f RCA jack shell. A 47K 1/8 watt 1% metal film resistor worked for me when I had excessive gain on my Parasound preamp  

Antinn,

I have to thank you so much for your reminder that the Benchmark had three gain settings. I have much more control and seemingly more headroom in the sound now.
Without your post I would  probably be caught up in some convoluted solutions, 
This way, all I had to do is flip a switch.
You made a big difference!

RV,

Thank-you for the thank-you :).  It was about a month ago when a similar item came up, but that time it was a Bryston amplifier that like the Benchmark had a selectable sensitivity, and the simple flip of a switch yielded similar success.  Enjoy the music!