The XTVA is an option but your radio needs a newer version of firmware to support the HHCH for the XTVA (probably but in some cases not). It can be mounted remotely and an extension added to the HHCH cable.
An ASTRO Spectra W3 sounds like what you need. The W3 uses a HHCH that looks exactly like the HHCH used for the XTVA. If you *really* need 700MHz support I'd look at the XTL in the same W3 configuration.
You can see the ASTRO Spectra W3 HHCH in this PDF. Upper middle.
Click here
XTL info
-Wayne