SPL meter results relative to Magnepan's (supposed?) craving for power/current

Hi all...
My thoughts are; if my ambient/background level is about 40dB and readings of "music" at my typical SPL from my listening position show about 75dB, that means that what I'm actually hearing is mostly noise and not my Maggies? Surely yes... Right? 

Even though my Maggies are in a very big room, do I need to rethink my amps power output of 400 WPC if I prefer a lower listening level? Overkill? I understand the benefits of "headroom" and amp/speaker "synergy".

At which SPL do your Maggies wake up and sing?
Thoughts? Comments?

Thanks for the help!
To answer your questions, I don’t know the frequency range of my meter. But it was inexpensive.

and the maggies are about 9 ft away..
        and thanks, MC! It explains a lot knowing that was logarithmic
so the amp is loafing at 75db 9’ away at listening position. You should try to improve the noise in room IF possible. I have a 20 db fan outlet that is clearly audible. You should also try to demo a lower power amp, consult to Maggie crowd..

@bdp24 will have excellent advice, he can hear and knows tge value of an spl meter..
An ambient noise level of 40 dB is very high!

My ambient noise level is 28 to 33 dB.

My Magnepan 3.6 "wakes up" at at around SPL peaks of about 75 dB.

But that depends on amplifier quality, 

A very high quality power amp can sound very good, late at night, when ambient noise is low, even at low volumes.

I agree that your ambient noise level does not sound right. My listening room measures at 12-14 Db ambient (Hvac Off). Using Tin Pan Alley as a test track, they "fill out" in a rich way at around 50 Db. My listening average is 60-65 Db. Interesting question, but I can not say how much of this is my getting slightly older ears :). @ 85 Db you almost want to leave the room and the amp isn’t close to clipping. 300W Bryston 4B3.

Edit: HVAC System finally came on and it measures 23-25 with air running.
With 400wpc whatever Maggies you have, they will sing. I'll assume that is 400wpc at 8 ohms. If not YMMV.