According to the manual for the DHC-9.9, the control for upconversion remains unchanged.

However, it should be noted that HDMI sources should NOT be upconverted in any case based on what the manual says (only S-video, composite and component sources are upconvered).

http://63.148.251.135/redirect_service.cfm?type=own_manuals&file=SN_29344765A_DHC-9.9_En_web.pdf

This is what the manual states for the DTC-9.8 as well.

http://63.148.251.135/redirect_service.cfm?type=own_manuals&file=DTC-9.8_En_A.pdf

Of course, this doesn't mean this is how it works in real life.