four speaker in spark LT model

I am based at Chennai. Purchased the spark LT model from Sundaram motors. There is provision of two small speakers at the back. I wanted to fix two big sony speakers at the back (removable tray). Dealer initially agreed and deducted the money to fix the speaker. Now he is refusing saying that GM has instructed not to fix four speakers in spark model as there is problem of short circuit. if you would like to fix, it is at your risk. If short circuit happens then you will loose the warranty. I would like to know Is it true?