You have a great system to start with. Prior to expending dollars, I would take the time to listen to different systems and get an idea of what your sonic preferences are. Ones best system/$$ is that one tuned towards ones own preferences. What you learn will be applicable regardless of room size. For now I would stick with your Marantz integrated and CD player and focus on speakers.
You will learn most by swapping out speakers. Given your current room size and that you have stands I would give a listen to different stand mount speakers that are compatible with your current integrated. You can buy used ones and sell them more easily as shipping costs are reduced. I once owned the paradigm 20s V.4 and liked them very much, however there are so many other good ones in same price bracket offering a different sonic signature. The idea of adding a subwoofer is credible.
One piece of advice, purchase a copy of Robert Harley's 'The complete Guide to High End Audio', 5th edition. Best $40 you will spend. Can be bought from Music Direct.
You will learn most by swapping out speakers. Given your current room size and that you have stands I would give a listen to different stand mount speakers that are compatible with your current integrated. You can buy used ones and sell them more easily as shipping costs are reduced. I once owned the paradigm 20s V.4 and liked them very much, however there are so many other good ones in same price bracket offering a different sonic signature. The idea of adding a subwoofer is credible.
One piece of advice, purchase a copy of Robert Harley's 'The complete Guide to High End Audio', 5th edition. Best $40 you will spend. Can be bought from Music Direct.