Subwoofer adjustment for each recording

The relationship your subwoofers have with the rest of your system should be stable. If the bass on a certain recording is too strong for you then use a bass tone control if you have one.
Well integrated subwoofers should not need any adjustment. Poorly integrated subs can be all over the place with different recordings.
I know what REL says. Their method of integrating subs is for people who do not want to spend any more money to do it right. The right way is to use only low level connections and a dedicated 2 way crossover like this one https://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4-hd.

Music from different eras ,ie, 1960's will have more bass than mid  to late seventies onward . I usually set my Rel:s and leave it until I play an older record. Life is too short to listen to music without proper bass Imo. It's the back bone of music I listen to

Does the statement "seems too strong" mean you don't actually enjoy the stronger bass on these recordings....or....you enjoy it but don't know if you are supposed to enjoy it?

For my two cents, the system/tuning/music should always be to what sounds good too you and not to some supposed what the recording engineer intended.

Also, I suspect that people often adapt to the recording that have stronger bass, get used to that stronger bass and then wonder if other recordings have too little bass?

Some recordings have a lot of bass. Sometimes when you go to clubs and hear music live, there's a lot of bass. Other times, other recordings, there isn't.


I like to play the recording and have it sound like it was made.

I just put remote volume control before my sub array.
Do what you want but rest assured that it has ZERO relation to a loudness control, which for other purposes, is simple to build. PM for details.

It's hard not to adjust the bass to your own liking but you should tune your bass for a natural sound. Some recordings will have more or less bass than others. Back in the day we set our rigs up and just let it play. 

Right. Because, bass perception is highly variable and this is even on top of recording levels. The same music that seems to have too much bass will sound just right at a lower volume. This is where the Loudness switch came from, to turn bass up a lot so it sounds right when listening at a lower volume.

What this means is you have two choices. One, you can mess around constantly tweaking level from one song to the next and every time you change the volume. Or two, you can listen to a lot of stuff just like normal and make a mental note how things sound. Then after a while if it seems on balance it would be better a little more or a little less make a very small - very small - adjustment. 

That is what Duke recommended, and that is the way I did mine, and it works great. Nothing ever is perfect, but overall everything sounds great.

Adjust at the preamp if you have that functionality. Otherwise leave alone.