Difference between amps

OK so let's talk amps.  I'm sure this has been addressed before but are there real differences between  multi-channel amps among the various brands in the mid-fi to high end markets with comparable specifications? Adcom, Anthem, Classe, Emotiva, Krell, McIntosh, Marantz, NAD, Parasound, Outlaw, Rotel, etc.  What are the differences in these brands?   I can site one difference.  In multi-channel Marantz amps, the specs never state "all channels driven".  They are notorius for misleading the consumer with their power output ratings.  But that's a marketing decision. What are the real or should I say physical or performance differences among these?  .  
@redwoodaudio  Check out the impedance of your speakers.


If you averaged it over the entire spectrum it would be well over 8 ohms.  Sensitivity is not the only measurement that matters.
@twoleftears that's my point... easy to drive, yet sensitivity under 90 dB (87 per stereophile measurements as you linked).  limiting one's self to "highly efficient" speakers over 90 dB sensitivity, without regard for other factors, would be senseless except when using flea-watt amps.
Thanks everyone for an excellent response and participation.  This has so far been a very active thread with very meaningful feedback.  I've learned a ton with many takeaways.  Although I do have a 7.2 surround sound system for movies, etc, music is still my first priority.  I listen mainly in multi-channel stereo.  One thing I learned here (and others have implied this to me but I forgot about it) is to use a separate higher output two channel amp for my mains and then a 5 channel for the surrounds and center.  I'm going to make this change right away.  Another thing is that for the $$, it seems Parasound is a super choice.  I may sell my Marantz MM7025 and purchase a Parasound two channel amp.    THANKS again.
I ended up with an ARCAM AVR 550.  However, I wish I could have afforded to pay $5,800 for the ARCAM AVR 850.  Their G technology is incredible, as the first 50 watts are pure A.  I had a real problem with their customer support and they are probably the worst in the business.  He was a real jerk and hid behind his phone.  Not sure what I would buy less because I want to be able to have an amplifier that can handle both 2 channel and home theater.  When the time comes I will call upon this group to help direct me.  
Hello PDN.  You almost never need more than 10 watts per channel. Receivers generally don't have power supplies that can really supply the "rated" 100+ wpc they might advertise. The gear sold in chain stores is made to a lower standard than so called "audiophile" equipment. That said, I have in daily use, multi channel amps from Emotiva (5 ch), Starke (4 ch), and Integra (9 ch). All get good to rave reviews and work beautifully for me. I don't know how many channels you need, but the Starke AD4-320 is absolutely fabulous and supplies four channels at 220 watts into 8 ohms, and 320 wpc into 4 ohms. I have two of these amps powering two 4 way speakers (one amp channel per driver, electronic crossover). Stick to a serious brand and you should be fine. My pal has a 7 channel Emotiva and loves it. Enjoy the music.