Question about power amp built in high pass filter

[crippledchicken]

I have the Parasound New Classic 2125 2 channel power amp which has a Flat-20hz-40hz filter switch. my speakers are the Polk Audio Monitor 70 along with a DIY 15" Dayton audio home sub tuned port around 23hz. my question is, if I use the 20 or 40hz choices on the filter since I have a sub, would this be a good thing to do to lesson stress on the power amp and maybe give cleaner sound or, would it add unwanted distortion due to putting the extra components in the signal path? I never run the system hard any way just trying to be sure to get the cleanest sound from my power amp and speakers. the rated response of the Polks is 40-20khz. Now the sub, gets it's input from one of the sets of outputs of my Adcom GFP 565 Preamp and at the time I run the Bash 500 sub amp at around 70 or 80hz on the built in crossover. Hope this is enough info and thanks for any advice!