Thanks to all for the responses.

So I don't have to put the HDRI's into, say, the 'content'  folder in the Bryce root directory, then? I can leave it out of the root directory all together? Correct?
I was mainly curious if Bryce had a required specific location that HDRI's had to be for it to find them.

Bryster,
the black materials I was referring to is the black materials on the object due to the lack of materials coming in with the object  when imported from anpther program, not the black place holders in the material library.

When I convert , say, a lightwave mesh to a format that Bryce will import, sometimes the mtl file doesn't translate into Bryce and all the materials end up being black on import. That very rarely - if  ever happened to them in earlier Bryce versions prior to 6.1.So I decided to go back from 6.1 to 6.0 and now I don't seem to have that problem.

Thanks again for you responses!

rstar