It is actually a TV/receiver problem. The HR24 outputs a signal using a 15-235 RGB color space (sometimes called RGB Normal)rather than a YCbCr color space which the other DVRs/receivers use. This should not be a problem since all TVs are supposed to automatically detect color space and adjust accordingly. However, it seems that all plasmas to a particular design (starting with the Pioneer Kuro and moving through some (not all) Panasonic and Samsung equivalents) have an issue in that they don't detect this correctly, and the result is that black levels are all screwed up and (for some unknown reason) people also report loss of sharpness. You can get the same issue with some A/V receivers when you passthru the HDMI signal to the TV.
There is apparently a setting on the TV for black level where you can manually set the TV to expect 15-235, but I don't have one of the problem TVs so can't confirm that. The only other solution is to replace the HR24 with one of the other DVRs which don't output 15-235 RGB. As far as I know,the other HR2x series all output YCbCr. Don't know about the HR34 though.