These are my recommendations. Are your 6x9's old? Because, they are cheap speakers, but they still shouldn't distort like that. Some good 6x9 http://www.amazon.com/gp/aw/d/B003KN2TGM/ref=mp_s_a_1_6?qid=1398354095&sr=8-6&pi=AC_SX110_SY165_QL70

Some good 6.5" rounds http://www.amazon.com/gp/aw/d/B003KN2TF8/ref=mp_s_a_1_4?qid=1398354234&sr=8-4&pi=AC_SX110_SY165_QL70 Finally you said you wanted to maybe add a second 15"? This amp has 2 channels, so you could add the second some at any time. As for knowing if it is 2 or 4 ohms, you can use a digital multi meter (dmm) to measure the impedance in the sub. This is a 2 ohm amp, but a 4 ohm isn't hard to find. http://www.amazon.com/gp/aw/d/B003CYL7LW/ref=mw_dp_mdsc?dsc=1&qid=1398354444&sr=8-12 I hope this helps!