I've an existing Home Theater system with a 5.1 Setup.
I'd like to upgrade to 5.1.4 , so will it work if I connected the existing home theater to A/V receiver by HDMI or Optical Cable , and then connect the ceiling speakers directly to the A/V receiver ? and if this could work perfectly, what would be the best model to use a 5 , 7 or 9 Channel Receiver and what;s the recommended model then ?
You can't use your old 5.1 HT electronics with a new receiver. You could use the old speakers.
You will need a 9 channel receiver and 4 ceiling speakers in addition to the 5 speakers you already have to get 5.1.4. Everything connects to the new receiver. If your old system doesn't have a self powered subwooofer then you will need one of those too. Standard AV receivers never have amps built in for the subwoofer. HTS packages almost always use passive woofers. You could buy an amp for the passive sub but it's not likely to be as good as just replacing it.
Specific receivers would depend on what your budget is. Onkyo/Pioneer or Yamaha for entry level. Denon and Marantz at the next level.