I need help with the audio side

I am a novice as far as high end audio and would like to upgrade my current setup. I have upgraded over the years from an older Bose Lifestyle 12 system (I know I just made a bunch of you cringe) to a Lifestyle 28 system. Then I learned that no highs, no lows, must be Bose and upgraded to a Harmon Kardon AVR 340 with Infinity TSS750 7.1 system. I have stayed with the Infinity's but upgraded the receiver to an Onkyo 804. I have it all tied into a Monster 3500 Power Center to try to clean up the power and used Monster XP speaker cable's and 1000 series HDMI and optical cables to connect the cable box, Samsung BDP1200 bluray, and Roku Soundbrige M1000.
My system sounds decent but I know it can sound better. Way better. I have listened to Definitive, Vienna Acoustics, Boston Acoustics, Polk, and Martin Logan and fell in love with the ML's and how clear and precise the sound was (like what I was listening to was live in front of me). I was looking at replacing the front 3 speakers, but would like some advice on brand/models to look in to. I am on a budget, so I know some of the extreme high end like Wilson audio is probably out of the question. I also need some advice about preamps and amps...mainly do I need them? Can I use the Onkyo as a preamp and maybe just get amplifiers?

I watch a lot of movies, but also love music (I listen to mostly everything except country and would say Pink Floyd is my favorite).

Any suggestions?