David, you have an RF Modulator in the BV7 but it requires amplification via the external RF amp.
Simply terminate you existing aerial feed to the Avant where you are going to site the box (in the loft/roofspace/cupboard) into the RF AMP (AERIAL IN); then use the remaining cable feed (which was the aerial feed to the Avant now terminated at the RF LINK AMP) as your MOD(ulated) SUPPLY 1.
At the TV placement end the cable arrangement remains the same, Aerial In still therefore goes to Aerial In, and your Modulated Output goes to your RF Amp and distributes accordingly once you have connected the other TV output feeds from the Labgear. If you have only a further three TV points to be fed it may be better to connect them directly to the RF Amp (I recall 4 modulated Outputs) and leave the Labgear out all together (it can be used in conjunction with the RF AMP if you need more).
You'll need power to the RF Amp and 4 or 5 Sat F-Plug connectors.
I would have responded by email but at least this might be of benefit to others, RF Amp offers better quality than the internal Avant RF Modulator.
Ian