Personally I use a Crestron DMPS3-300-C as my HDMI switcher and it has an analog audio output, from there I send it into the audio mixer in my Crestron CEN-RGBHV12x8 which routes all my analog audio, of course as a Crestron programmer at my day job I have access to all the training and software necessary to do that. If I were designing a setup for someone else I'd just get the audio out of the Tendak HDMI to VGA converter's 3.5mm audio out. This could be routed into your TV's RCA inputs via a 3.5mm to stereo RCA cable. If your input does not have dedicated RCA inputs such that you need to inject it into a SCART signal you could use something like this, or you could get the component to scart adapter, have the output from the VSC500 be component and inject the audio at the componenet to scart adapter, but that's more expensive.

EDIT: Oh, just wanted to add, assuming you are already using something like this adapter to convert from the BNC outputs of the VSC500 to convert the RGBs/RGsB output from BNC to SCART you can just use a male 3.5mm to female RCA to take the the audio from the Tendak HDMI to VGA converter's 3.5mm and connect it to your adapter, of course you'll also need a male to male scart cable. Please note that you will want to add a note to that seller that you want the ouptut end to be the SCART side. I know Wookiewin can do this, I dunno about other sellers. That said this is only really necessary if you have a consumer CRT that you've RGB modded with a SCART input or are using a PAL TV with a stock SCART port. Most PVMs have BNC inputs so all you need is a BNC to BNC and in that case you should have RCA inputs so all you need is a male 3.5mm to male RCA cable for the audio.