Old Classical Recordings

I was wondering if somebody could help me with a problem I've just encountered.

I'm listening to a recording of Hans Knappertsbusch conducting the Wagner Ring in 1956 (Label: Orfeo). I noticed that if I turn the volume up, the voices start . . . clipping seems like the best word. Especially with the soprano, it seems to overload and you end up with a sort of tinny buzz.

I haven't gotten this sort of response on any other recordings before. It doesn't sound like the amp is out of power because the bass sounds fine. I was wondering if this is something that older classical recordings tend to suffer from? Is there anything I can do to help this? I was thinking that part of the problem might be the CD player I'm using, which is an old Marantz from the early 90s - perhaps the filtering is having problems resolving the high frequencies through all the noise.

Thanks for any help you can give.