There are various ways you could do this:
Using PMW, you could use Library Tools->Convert Format with DSP options (eg Adaptive Volume) to permanently alter the files for a louder volume. (Not recommended)
OR you could use the DSP options during Sync to do the conversion only during the transfer, leaving the originals intact.
Or, using JRiver MC (which can also write to the Pono) you could use the DPS Parametric Equaliser to boost volume, which isn't in PMW.
One of the things I do for car transfer is use the DSP to Volume Level everything (using R128 data from Analyze Audio) and then boost by +6dB. This levels all tracks and then restores 6dB of volume. This does risk clipping on some tracks, but for the car I find it's better to have volume encoded as my volume knob runs out of "power" otherwise. Similarly with the Pono, I find myself running near full volume often enough that I'd not want any extra attenuation in the source files.
Anyway, PMW/JRiver gives a huge amount of control over volume options such as this. It's just a case of exploring the software to uncover everything
