Hi Dan, I see it's been a while since you posted, so this may be coming too late.
I'm designing an A/V system for a small meeting building for our church using Home Designer Architect, and I can say there is virtually nothing useful in the product specific to Audio/Video systems. There is a Home Theater library, but it is mostly for furniture and fittings. I have not been able to find any libraries that help in this way (but maybe I'm missing something). With a more advanced product (Pro, Chief Architect) I gather I could create CAD objects for this, but it doesn't seem to be possible with HD Architect.
For the plan views, my solution is to use standard Duplex outlet symbols, changing the label to "SPKR," "MIC," "HDMI," etc. You can then use the Connect Electrical tool so show the connection points. Of course, on the plan view, they still look like a duplex output, but that's something I'll sort out with the contractor. I have also added a "NOTES:" text box to the plan explaining that all HDMI runs must be 1-1/2" conduit, and it will be up to the contractor to determine the routing and placement.
If you want to show wall elevations that indicate where the junction boxes go, again, they will show up as duplex electrical outlets. In this case, you'll have to take a screen capture and edit the receptacle plates in a graphics program to show what you want.
In the basic library, there are some entries in MEP>Electrical>Jacks for CAT5, phones, etc., but they are indeed basic. The TV connectors all show cable TV-type coax connectors.
All in all, it's a bit of a pain, and I hope the folks at Chief Architect Software will consider adding some basic support for today's common residential A/V wiring.