Gonna hook them up in series for a 2 ohm load, With the amp being 600 watts rms and the two subs only being 300 rms, is that too much power for the subs to handle?
If so, then yes you would get a 2 ohm load into one channel.
However, a lot of people recommend that you get an amp that puts out slightly more power than what your speakers can hadle for headroom. Slightly more power being no more than 20%. So at 600 watts, no more than 720 watts.
I am just stating the fact that it is good to have headroom (extra power).
I am not suggesting that he get rid of his amp and get a 720 watt amp.
Headroom is protection for the amp. It is not a goal for the speakers to meet.
Just because a given speaker is rated at 300 watts; doesnt mean that you have to play it at its max all of the time. It also does not mean that you need to match it up with an amp that is suitable for its maximum power handling. A matter of fact is that you only need like 5 watts to enjoy your speakers. Anything above that is just amplification.
The only reason people believe that you should match a speaker to an amp that can produce up to 20% more power is so that knuckleheads that have no self control do not ruin an amp because of mis-use, and then turn it in for warranty.
lol