Sipura 2000 Network Help Needed

We are thinking of installing up to 10 Sipura 2000 devices in our call centre to allow up to 20 agents make calls over our ADSL line. Currently we have 20 ntl analogue lines.
Currently we have 20 PC’s on our network all connected to the network through ethernet cards. The vendor that is supplying our Sipura 2000 units has told me that we should buy a splitter to split each network connection to allow one split to the PC, the other to the Sipura 2000 unit. However my PC/Network supplier has told me that this may cause conflict on the network as the router may not be able to assign IP addresses “effeciently” and the whole network may crash.

I am looking for some advice as to if it worth the risk to invest in the Sipura 2000 units or do we need to do something different on our network to allow the whole thing to work properly?