Thanks a lot for the advice! I will try Rothwell attenuators. I guess a "source" option would be a better choice, as I will be able to connect them to the output sockets of the DAC and it will not affect other sources.
Yes.
Unfortunately I think you may find you will lose some sound quality with the Rothwell's in place, especially with other lower output valves.
I definitely found that to be the case. It feels like you can't make up for what you attenuated earlier by increasing the preamp gain to compensate.
Therefore, the attenuation needs to be minor, and of the best quality you can find. Better quality, I think, than the Rothwell's provide.
That's why I went for the best resistors I could get i.e. the silver AN tants.
Try them, though. They're so cheap it is worth you seeing if you agree with me. You may not - but I doubt it