Can I get a better picture using using a HDMI connection to DVI input on the 990 than I can with component video ?
It depends on the source you are using. I've tried several HD cable boxes and found the difference between component and DVI/HDMI to be almost nonexistent, but with disc players it is possible to get better results with HDMI - especially those that have different processing capabilities at the HDMI output than at the component output.
Would I lose menu options on my Direct TV box and Oppo 980H if I did go with HDMI to DVI into the 990 then out from the 990 with component video to my display
The DirecTV and 980H would provide the same menu options and other controls either way. When using the 990's DVI output, you can't see the 990's menus - you have to use one of the analog monitor outputs to get that. There's one issue here that may simplify your decision, though: the 990 can't convert from DVI to component. It's actually a standard limitation even on newer hardware, as there are some copy protection concerns about converting the digital video signal to analog outside of a source or display. About the only way to make a conversion from HDMI or DVI to an analog video format is with a specialized product like the HD Fury converters. Which leads to the next part...
Is there a adapter that goes from HDMI to D-Bus connection ?
. My Panasonic has one each, Component video , Composite Video , S Video, RS 232 and D-bus conection.
I know they make a HDMI to DVI connector, and a DVI to D-bus connector, but can not find a HDMI to D - bus
When you say "D-Bus" I think you are referring to "D-Sub", which is another name for VGA. It's a 15-pin connector (three rows of five) used for computer monitors. This is an analog video connection. You can sometimes get converters for component-to-VGA or VGA-to-component, but you'd need an HD Fury to go from HDMI to either component or VGA.
When you've seen DVI to D-Sub connectors, they have been using DVI's unique computer legacy: the full DVI spec includes both digital video (DVI-D) and analog video (DVI-A) inside the same connector and cable (called DVI-I when it's all lumped together). The adapters grab the pins for analog video and convert it to VGA.
Your Panasonic doesn't have a digital video input.
That makes the decision easy: stay with component video. It's the simplest and most efficient solution for your case.