How to unleash the optimum power of a receiver?

audio video receivers are, ultimately, going to yield you limited power distribution, as compared to better separates based systems, everything considered. Not knowing your speaker models - unless your main speakers offer at least powered woofers - my first thoughts are you will get advantage in running whatever speakers you have at 80hz on your receiver (even if they're full range), and letting a powered sub do the bass. Dynamics will most always improve greatly, and the system will be much more efficient, less taxing on the receiver to be certain. Yes, you must ALWAYS anyway consider making sure ea speaker is placed properly, and the system set up well as a whole.
So, yes, I'd focus on making sure the system is set up to maximize the sound, so do your research here.
Also, adding an outboard amp will greatly help your situation.
BTW, does your receiver have audyssey? If not, the newer will do better for your acoustics in helping smooth things out (remember to not place speakers in acosutic "holes" to begin with, as you can't fix that with an EQ). It's a thought. Staying with things as is, it's settings, speaker/seating placement and acoustics, basically. Adding better amplification yields an easy 100% improvement in soujnd, most always, as well! However, to be true, running your speaker as small does make for a much improved sound on it's own, as opposed to running full range.
What model speakers again???
Another thing is to amek sure you have matching speakers up front, at the very least, and then ideall matching all around if you can.

Btarianto, I believe the -25/-20 dial on the master volume that you refer to really does not mean much about the quality of the sound. If this is your concern, the best thing to do is to get a RadioShack SPl meter to set your SPL level at optimum and to balance the sound level of your speakers. In a 14x16 room, when I using the MACC on my Pio SC05, my FR/C/FL was calculated at -5db ( in range with the level of 75db/ C weight on the SPL meter) and the result is I have to dial up the master volume to 25/20 but in a whole, the sound quality is much more balance. Interesting enough, some of the salesman at local store boosts all the speakers to 0db manually and as the result, the master volume does not have to crank up higher to give customers a sense of false "powerful amp". I asked one Bose rep why did he do so, he simply replied :" it sounds better". Not, louder is not better. Quantilty vs. Quality. Go figure.

I am listenning to my budget Pio A35r intergrated right at this moment. At 45WPC, at the same set up ( speakers, source, cables...), the Pio A35r intergrated at between 10 and 11 o'clock position sound much louder and more musical than my 130 WPC Ice power at -25 dial on the master volume. A $200.00 intergrated vs. $1,800.00 AVR in 2 channel audio playback ....Just a thought about your concern with your master volune level so I take note.

Placement within your reason/available space, balance all channels to same db level, and if using a sub...use a good one (svs, hsu, velo, ED, JL). Some damping in room (sofa, drapes, pillows) as well as some reflection from walls/ceiling. I do believe you can replace pwr cable (signal here at the gon). If recv'r is calibrated to reference your vol indicator lets you see at a glance approx level compared to reference level of about 105db. This is based on Dolby/DTS reference level for movies. Remember, it takes a doubling of output pwr to increase 3db...thus at a -24 level you are wwaaaaayyyyyyy far from amps capability when it is going to take twice the given pwr to go from -24 to -21...got it? Your 2805 tops out about +16 or so...perhaps +18/+20. Friend has a **02 series and my son has a 1602 in his ht rig I put together for him. Theirs go to +18. Anything past 00 would hurt you or small creatures in the vicinity if setup properly. Use the auto setup feature for spkr distance and level calibration if you have the mic that come with it. Otherwise as advised, use test tone and adjust ch trim so that all are same on spl meter reading 75 db with master gain set at -10 or 85db with master gain set at 00 which most people find much to loud/annoying. I advise -10 on master volume knob and adjust until the test tone reads at 75db on spl meter so you don't damage your spkr drivers.

I really don't think you need to look at your receiver to improve the sound... if I understand your post correctly, you are using mismatched speakers (Jamo w/ a couple of Definitive Tech's); this quite often leads to mismatch as the sound pans around you. I would replace the DefTechs (although DefTech does make some great products!) with a pair of matching Jamo's to keep the sound coherent.