Digital BW, The Print

In reading some of the Piezography K7 documentation, I read that files should be in Gamma 2.2 profile and that I should change the Photoshop grayscale color space to Gamma 2.2.

That's all well and good.

However, I have numerous grayscsle files with an embedded Dot Gain 20% profile.

The Piezography docs says "as a rule, you should never convert a grayscale image from one profile or gamma to another in order to keep the smoothest tonal transitions possible".

This seems like a Catch 22. 

Don't a need to convert my files from Dot Gain 20% to Gamma 2.2 before printing?

And, if so, should I select "Perpetual" or "Relative Colormetic"?