I don't think the term noise floor is used correctly in this scenario. Noise floor implies that it is the device noise that is constant regardless of signal level.
In the Windows envrioment, let's say the noise has a value of 1 and signal at 10% volume has a value of 1, the SNR is then 1, very audible. At 100% volume, the noise "floor" is still 1, but now your signal has a value of 10, and the SNR is now 10, much less audible. By introducing a attenuator after this, of course the noise is attenuated, but the signal is attenuated too. So the SNR is, regardless of your volume adaptor, 10.
Adding the attenuator does not decrease noise floor. It decreases the noise amount, and at the same time, your music as well.
The noise floor is constant regardless of Windows volume if my attenuator is set to 15%. If I lower Windows volume to 10% and max out the attenuator, the noise floor is constant regardless of Windows Volume (same as if I connect directly, without attenuator. It is all over the forum that the attenuator reduces floor noise from high output impedance sources, it is a well known fact lol. I don't know the science behind it but it is definitely not a subtle difference, it is huge, reproducible and very easily noticed. That is particularly why it is included with these 9ohm IEM's which pick up floor noise from almost every desktop amp
From Shure's official description:
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Level attenuator offers precise volume adjustment and comfortable listening to playback devices, including airplane headphone outputs that are often too loud at the lowest volume setting. Reduces the level of incoming signals and background hiss.
the little tiny problem with you plan I would say is that your remote volume attenuator is most likely a variable resistor ^_^. the lower you set the volume the higher the impedance. I=U/R the bigger the resistor, the lower the loudness.
for the hissing that will work perfectly, you increase the volume from your sony, and lower it back with the remote stuff. making the difference between the hiss and the music higher, and so the hiss less audible.
from an impedance perspective it is very bad news. you will completely tilt your signature on the 846. the higher the source's impedance, the more bass and less trebles you will get on the that IEM.
think that with more impedance the IEM signature will be more and more a superposition of the original signature and the impedance curve(line at the bottom). and with values so low, the change will be several DB after even a few ohm(and most likely you would need close to 100ohm to get almost rid of the hiss).
so if you like your 846 with more bass you can try this, and even change the filters to get a little more margin. but if you already have too much bass, then only an amp can do the trick of low noise and low impedance. (I wouldn't worry too much about damping factor as a way to control the drivers, BA drivers are so efficient I doubt that would be a problem, only the signature of the IEM will be).
the hissing misunderstanding comes from the fact that noises can have several origins. on a DAP, it is most likely that the noise we get is from the components and unrelated to volume. so if the noise is 40db loud, and you listen to music at 80db loud, then you have a hiss just 40db below music. now if you listen to music at 100db, that hiss is still 40db loud, so it is now 60db below music.
that is the logic used with the volume attenuator(variable resistor). you increase the DAP's volume by a lot, making the difference between the hiss and the music huge. then you use the remote to reduce the overall loudness to get the music back at 80db, but this time the hiss will also go down with the rest.
that's how it works, and it isn't a problem when the headphone has a flat impedance response and not such small impedance values. the SE846 is probably in the top 5 list of universal IEMs that will be greatly affected by the source's impedance(and source for the driver is amp+cable).
now maybe they have made something amazing that keep the impedance low with the shure remote? I don't know what that product is, but I wouldn't get my hopes up etheir.
