RGB connection basically means better quality picture because the three colours that make up the TV picture (Red, Green and Blue) are sent separately, no coding/decoding to be done. I am assuming that the V.Tape SCART socket doesn't support RGB (probably only intended for a VHS recorder) and therefore you are not using RGB at the moment. I would suggest you get out your TV manual and check the specification of both the TV SCART sockets, you may benefit from a different connection scheme. Without knowing more detail you might find this better.
DVD > Humax VCR SCART
Humax TV SCART > TV AV SCART
If the Humax is in STANDBY the DVD player will connect to the TV. If the Humax is ON the DVD player will override when PLAY is pressed. Both will be able to connect to the TV with best quality.
