Yes, the SansAmp Bass DI has an input impedance of 940K ohms, suitable for use with piezo double bass pickups.
I suspect that your friend is suffering from an impedance mismatch problem, which results in the thin, bassless sound with brittle highs - not a good bass sound. For a more complete explanation of the effect and reason, see the bottom of my Preamps Page -
http://www.gollihur.com/kkbass/preamps.html
I have taken my SansAmp Bass DI to festival gigs where I ran my Kay/Bass Max to it, and the sound guy took the output and was fine with it, though initially was perturbed when I told him I preferred my DI to his. Of course, I returned his to the signal chain when I left the stage.
I had previously run the Bass Max/Bass DI through my own PA, set to flat EQ, in a quiet setting, so I could find the best settings on the DI to produce the desired sound, and that way can preset the SansAmp to that reference setting. More frequently I use my own amp and the sound guy takes a line out from the Contra or the Eden WT300C I previously had. I've also plugged my K&K Bass Master Pro preamp's output into a DI, and also direct to a PA.
The SansAmp is good, as I mentioned, but it depends on the venue. If they have an active sound man, I don't feel uncomfortable with sending my reference sound to them - the volume and tone are their problem. However, if I am gigging where it's our PA, unattended, I do like to have a K&K preamp on my belt, easily accessible so I can easily make volume changes, or even tone tweaks if necessary.
I will bet if you plug your friend's bass into an amp, and then do the same with the SansAmp in the signal line, the difference (even with the DI set flat) with be dramatic, and you may have to wrestle it back from him. <g>