Be aware the VSX product line was end of sale in December, 2011. It will be end of support/end of life at the end of this year. The current product line from Polycom is the RealPresence Group series (GS), and the HDX product line was between the VSX and the GS.
In order for the VSX to host a multipoint conference you would need to have a multipoint license. the part number is 5150-21297-001, VSX MPPlus Multipoint Software Option Licenses for VSX 7000e, VSX 7000s, VSX 7000 and VSX 3000. Not for use with VSX 8000 Series. Allows for 4-site MP video calls.
You will need to make certain the site hosting the multipoint call has the necessary bandwidth to do it.
Alternately, you can purchase a multipoint MCU or lease the service from a video multipoint service provider.
Contact your Polycom reseller for additional information.