How much watts does this amp put out for 2 subs?

JBL CS300.1 is the amp(300rms). i have it hooked up to a 10" pg octane sub(300rms). i like the b but i want more, so if i get rid of the 10"sub and added two 10" or two 12" what rms should i be looking for if im going to run this jbl amp. also ur opinoion is it worth doing. cuz i think of it being two subs= 150 watts rms to each sub b.c the amp puts out only 300rms total. am i wrong?