Lowering the noise floor

However, before you can benefit from a lower noise floor in your gear, you will need to lower the background noise in the listening environment. I just measured mine at about 35 dB on a Sunday afternoon, and that is low. When the house was designed we did a lot to achieve this. At that stage it is quite easy and cheap, unlike afterwards:
1 a quiet location, in so far as such a thing exists in a densely populated country like mine, and in a (sub)urban environment.
2 special window glass
3 muffled ventilation openings
4 quiet floor heating system.
5 quiet mechanical ventilation system that is only turned on when needed.
6 quiet water pipe layout.
7 quiet kitchen machinery like refrigerator and dishwasher.

It all makes a difference, but even then it is not concert hall quiet, and since maximum sound levels cannot be as high as in a concert hall, the dynamic range is inevitably smaller than in that concert hall.

Sure but if for whatever reason the noise floor in your room is high, it will mask any noise from your electronics. Given the noise levels involved, this is not just a theoretical problem.

Once again a lot of voodoo science, and some suggestions that may have to do with sound quality but not necessarily with noise levels.
If you want lower noise levels (i.e. greater S/N) to increase dynamic range and detail resolution there are a few things you can do:
1 lower background noise (see my post above). In real life this is probably the most effective option because it is backgroud noise that masks the usually pretty good S/N performance of modern electronics. There is no point in listening to low noise gear if you are living next to an interstate with the windows wide open.
2 If you still think you can benefit from lower noise levels, look at the parts of the chain that have the worst S/N: FM radio, Phono inputs and rca interconnects, in that order.
FM radio is terrible with typically perhaps some 70 dB S/N, and there is nothing really you can do to get it close to the quality that can now be achieved by e.g. internet radio.
Vinyl and the necessary phono inputs are much worse than digital sources and line level inputs. Go digital and you have a far better S/N ratio. On most amplifiers the difference in S/N between phono (80 dB if you are lucky) and line level inputs is at least some 10 dB, which is not surprising given the amplification that is required, combined with the massive RIAA equalization.
Using balanced vs rca interconnects usually improves S/N by some 5 dB or more. Since these are typically used between a DAC/preamplifier and a power amplifier, we are already dealing with noise levels better than some 95 dB which is so good that the improvement may not necessarily be audible. But if you want the best, this is the way forward.

No it is not. FM has serious limitations, even if internet radio has as well, and they are of course hard to compare directly. FM once was a big improvement over and above MW, but it has quite a few limitations. First, there is S/N, second there are relatively high levels of distortion and third there is only limited channel separation. As a consequence, no FM broadcast is done without (these days automatic) dynamic compression, in the best cases only to a quite limited extent, but quite often rather invasively.
Compare that to internet radio. There is no need for dynamic compression, nor does it suffer from any of the other compromises inherent to FM. On the other hand there is of course data compression, sometimes rather badly, depending on the bit rate that is chosen. However, the algorithms that are used are marvels of psycho acoustic technology with exceptionally small reduction in sound quality, particularly at the higher bitrates. BBC Radio 3 is broadcast in 320 kbps and their and others' research has shown that this is virtually indistinguishable from full Red Book CD (there are quite a few blind tests on the internet to take yourself - few people can identify above 256 kbps). Even so, the BBC is now experimenting with full red book CD internet streams in FLAC (i.e. some 600 kbps depending on the type of music). So, the comparison is between the kind of signal degradation from the FM technology and the degradation from data compression of the digital stream. In my experience (with  an excellent FM tuner and good signal) the sound quality of internet radio at the higher bit rates that are increasingly common is significantly ahead of even good FM. That is the conclusion of the BBC, and I could not agree more. Moreover, the good news is that bit rates have been and are going up all the time.

Some reading material: https://www.quora.com/How-does-the-sound-quality-of-a-same-song-broadcasted-on-FM-Radio-compare-to-M...

I am going off topic now, but that level incompatibility could have been cured with a very simple set of inline attenuators.
And I fully agree with your desire to reduce room modes, even if I would not classify them as noise but as a deviation from the ideal frequency response. I have been very succesful with an Antimode 8033 room eq.