Just following on from what the guys are saying about the low-end 'mud'..... I've a hunch it's the way you're hearing the material which is presenting you with problems. The sound you have seems pretty consistent with less-than-ideal monitoring and until that bit is addressed, you'll really struggle to get the clarity you need. Most of us have been there. For those on a budget, it may be an idea to consider getting a good pair of headphones and something 'clean' to drive them until such times arrive to invest in proper monitors. If one can hear accurately, one can mix accurately - and the mixing process becomes a whole lot more enjoyable and less time is spent agonising in self-doubt on whether something sounds right or not. I hope this helps a bit :o)
EDIT --- Just noticed the bit about the 'bad' headphones.
EDIT --- Just noticed the bit about the 'bad' headphones.