i say get rid of those speakers and buy some cheap ones! ive used kappas before and they NEED an external amp to push em nicely. u have two choices:
1. use the H/U and get crappy sound at crappy volumes
or
2. get another amp and be blown away by the infinity's ability to produce bright as crap hurt your ears highs IF and WHEN u get that good, clean power
even a small amp like 35x4 will do. it may seem like "only 10 watts more than my H/U" but its good, clean, dedicated power and WILL make the biggest difference in the world
OR, you could just get some crappy pioneer or sony speakers that'll be more suited to using ur H/U power....
..kinda weird tho since the sensitivity on infinitys are really high