I received another signal converter today, the Ambery HDV1. I had ordered it last week from Ebay. It is not in the same price range as the model from Central Computers that I tested over the week-end - about 3 times the price - more with shipping and sales tax. It also has the interesting property that it works ! I connected the VGA output of the Roland VS-2400CD to the VGA input of the HDV1. I then used a DVI to HDMI converter, and an HDMI cable, and plugged them in to the DVI output of the HDV1. The HDMI cable went to port #1 of my Monoprice HDX-501 switch. And my Gateway FHD2401 displayed it nicely.
The HDV1 is supposed to support up to 1600x1200 resolution, which I have not tried, since the VS-2400CD will only output 640x480. But it could be useful down the road to hookup other VGA stuff, like my boyfriend's laptop.