Will something like a Linksys SRW2016 do me any good?

I've been using Vonage for a couple of years now.

I have two ATAs -- a Cisco ATA-186, with both a voice and fax line, and a Motorola VT1000, with a single voice line.

My network is configured so that I cannot use the Motorola as my router.

The basic blue print looks like this:

Historically, call quality has been fine, and faxes, for the most part, make it through. But, as my bandwidth needs from the PCs have increased, as have my simultaneous phone calls (it's common for both voice lines to be in use), call quality has suffered. In particular, people can hear us fine, but we have a hard time hearing them -- lots of stuttering. I believe we have enough bandwidth (768/256, soon to be increased); it's just not being allocated appropriately.

So, we are thinkng about replacing the old, unmanaged switch with a QoS-aware managed switch. The Linksys SRW2016 has caught my eye.

So, can such a device help us? If so, do we need to do anything 'special'?

I have no idea if these old ATAs tag the VoIP traffic for QoS. Anyone know?

If they do, will the SRW2016 'do the right thing' out of the box, or will we have to configure it to react to those tagged packets?

And, if one or both ATAs is NOT tagging the packets, can we solve the problem with this switch anyway? From where I sit, the needs are simple -- I just want to two switch ports which have the ATAs connected to get priority over all other traffic. That should be easy to acomplish, no?

Or, is the fact that the stuttering is only heard on our end indicative of a problem which cannot be solved within our internal network, and must be solved by our ISP?

ANY suggestions/recommendations greatly appreciated! (Even a recommendation for a different switch -- we are looking for 16 ports, and we like managed devices.)