Does the volume coming into a DAC matter?

Help me out I can't quite wrap my brain around this one. I've got a number of DACs, some are in integrated amp components other stand alone. When hooked up to my laptop I noticed that with some, but not all of them, changing the volume on my laptop changes the signal strength. But, I thought we were just passing data over USB to the DAC to interpret and create an analog signal from. Therefore my assumption is that the volume is just another piece of data, and it's not actually changing the signal strength. So is there an optimal volume to set the inbound signal to a DAC? Or does it really not matter?
If you are using analog outputs, then you are right, the signal strength ( peak to peak of the voltage) is varying.

If you are using USB it will not. The stream of data is conveyed in the difference between two lines, and must be 200 mV or greater to convey a 0 or 1. More here:

Altering the volume in a digital stream is altering the stream of 0s and 1s, but the peak to peak or differential of the voltages remains the same.


Thanks! That was my assumption. I'm also curious if there would be any performance difference as you move down the based on up steam volume choices. I guess the obvious consideration is that the less signal strength the eventually preamp or amp has to use the harder it works and the better the chance for noise. Like if my laptop is at half volume and the USB connected DAC respects that and passes lower signal onto the amp. 
The biggest issue I know of is usually with how much a laptop's' mixer will alter the bits unless it is using exclusive mode, and sometimes even then you still require special drivers. What is the point of having a super expensive DAC if the data it is being fed has been significantly altered already by a less than careful process?

Yes, in general, if you can feed your preamp full-range signal, you are going to end up with less noise and distortion than if you feed it a small signal you have to amplify.

Having said that, I do use Roon's EQ features a great deal, but it is relatively careful, uses 32 bit math, and I do the volume control in my integrated amp.
erik_squires That's really interesting. I tend to play audio from multiple sources (local FLAC files, Spotify, Chrome, etc.) so it sounds like I'm likely getting a signal that's already been monkeyed with by the OS (mac in my case). I'll need to look into that. 
I use Amarra SQ+ on my Macbook to stream Spotify to my Benchmark DAC3 with volume control. SQ+ is an audio driver and intercepts all music sources and streams bypassing the OSX core audio. This is how they recommend using it:

We would always recommend setting volume control at it's highest level for all apps and devices except for the last in the chain. Use that volume control to adjust listening level. This will make sure that each car in the train is delivering it's best signal to the next car in the train.

So I have SQ+ and Spotify at full gain and use the DAC3 for volume control.