Will adding an amp make a noticable difference?

I have a Harman Kardon AVR335 7.1 receiver which is rated at 55wpc.I am building a 7.1 system that currently consists of Paradigm 7SE MK3 for fronts and Paradigm CC300 for the center. As I find them, I will be adding side and back surrounds. This system will be used 99% of the time for multi-channel music. I listen to a wide variety of music and if by myself I like it fairly loud. Since most multi-channel music at this time is 5.1, should I be looking at 5 channel amps now and add another when 6.1 or 7.1 software becomes available? And I guess maybe the first question should be, is adding an amp going to be that noticable? If yes...how many wpc of an amp should I be looking for and what brands? More than likely I would be interested in used. Thanks for your input.
I don't know a lot about your specific equipment, so take this with a grain of salt. I'm assuming the HK has pre-outs, such that you can use an external amp? Assuming you can, I would guess that you'd hear a very noticeable improvement by buying upgraded amps, somewhat dependent on your budget. I would probably buy a really nice two channel amp, or mono blocs, for the L/R front channels, and then a five-channel amp for the C and surrounds. A cheaper alternative would be to buy a 5-channel amp now, and add some decent single channel amps as necessary.

You'd have to give more information about your room, etc. to advise on amp specs - in general, it's not the watts as much as the current the amp can produce. Depending on how difficult a load the Paradigms are, and how big your room is, the wattage necessary could be anything from the 55 wpc you currently have to significantly higher.

Does the HK have Logic7 decoding for creating a multi-channel playback from a 2-channel source? I'm assuming it does - if so, and if that's what you use, that's good - it does a great job for creating multi-channel music.
Post removed 

Thanks for responding. Yes the HK has pre-outs and Logic 7 decoding. I also have a cd player that plays DVD-Audio, SACD ant DTS cd's. The room is 17' wide by 24' deep, carpeted floors, walls are wainscotting (wood) lower 1/3 and drywall above. There is a dropped ceiling in the room that is made of 1" thick metal and it is insulated.

Not knowing what your budget is, you might try the following:

1. Add a multi-channel amp that at least has three channels (for the front three)
2. Mod your source with some basic upgrades (caps, dampening, diodes, power supply tweak, etc.)
3. Upgrade the crossover networks in your front three speakers

Really depends on your budget but doing those three things will make a noticable difference.

Absolutely, I added a Mcintosh MC352 to my HK AVR7200. The sound improved dramatically. Think about the cost of your HK and divide it by the number of amps (7), not to mention all the bells and whistles with the HK. You're probably looking at around 100.00 per amp (guessing). It would be great if you could find a good amp to try, if not you could always take your receiver to an audio shop and have them hook it up to something for you.

Good luck