I have a Dynacord Powermate 600 deck, which is a 600W deck.
For gigs I usually just connect two EV-300SX speakers. I'm now looking at getting a pair of bass bins to give a better low end.
If I was to get bass bins, would I need to upgrade the deck aswell as it's only a 600W deck or would I have enough power from the deck to power the bass bins and the regular speakers?
And yes you would.
Currently even though you have a 600 watt desk (300 x 2), it's only delivering 150 watts a side into your 8 Ohm Speakers. What you need now is a set of bass bins, which are also 8 Ohms and that have a crossover built in. That way what will happen is your Desk (Not Deck) will see 4 Ohms a side now instead of 8 Ohms, and you'll have your full 600 Watts. You'll feel a noticable increase in power from actually having an increase in power, but also from having additional low end.
I'd buy matching bins as per the spec above, see does it now meet your requirements, and if you're still not happy, then look at getting separate crossovers/poweramps.