Hi SamuelHi Raman340,
Yes the Marantz 4001 can handle 4ohm speaker load but I personally don't recommend cause it may affect its performance in the long run.You wont have much problem driving with 6ohm speakers though.
Music & Movie sounds are very dynamic,A 4ohm speaker can go much lower than its rated impedance.So an Amp rated at 8 ohm can easily handle 6 ohm,4ohm & may be lower too...But when handling lower impedance continously for a long time the Amp gets hot and can go into thermal protection mode for a moment.
So 8ohm load ->
6 ohm load->
4 Ohm load->
2 ohm Load->
Anyways Enjoy & be happy
Hv seen the 1708 & heard it too. Besides all what has been said, its bulkier than the 1707 & most importantly has HDMI which the 1707 didn't have. You can look at the 1908 also. At Fairdeal in B'bay the 1708 is priced at ar Rs 20K & 1908 at ~ Rs 24K. Value for money i wd say. I'm personally settling for the 1708 which i'll be buying in a week or so.