@edelbby Thanks for the correction about the Mac being solid state. If I understand the specs correctly, it is rated to put out 270 watts at 8 ohms, 4 ohms, 2 ohms, and 1 ohm. My Krell KSA 300S is rated to put out 300 watts at 8 ohms, 600 watts at 4 ohms, 1200 watts at 2 ohms, and 2400 watts at 1 ohm. I'm using it to drive a pair of Thiel CS6 speakers which are one of the few models that have as difficult an impedance curve as the Watt/Puppy.
David Wilson and Jim Thiel were unwilling to make the design tradeoffs that would make their speakers easy to drive. If you go to an audio show you will see Wilsons typically paired with D'Agostino amps or another brand that behaves like my Krell because that is the type of amp they were designed for and voiced with.
Your 7270 is a highly regarded amp and with the right speakers it will sound wonderful. But it was designed to drive speakers with a fairly flat impedance curve and there are hundreds of options to choose from. You don't need high efficiency horn speaker (you have 270 watts to play with) but you do need speakers with a resonably flat impedance.
There are so many excellent speakers available today, both new and used, that it is hard to make a recommendation. If you take note of speakers you think are candidates you should Google the speaker model and the word "review" and look for a review in Stereophile. The reason I mention Stereophile is because they always include the impedance curve in their measurements and they comment on what type of amplifier would be a good match for the speakers.
As a practical matter, either your amp choice drives your speaker choice or your speaker choice drives your amp choice. One way is not better than the other. If you want to stick with that gorgeous McIntosh then you want a speaker of average sensitivity that has a fairly flat impedance curve. Somewhere between 87 dB to 94 dB sensitivity would be good. You would not want an extremely high sensitivity speaker (98 dB to 102dB) that is made for low wattage SET amplifiers because you generally want to run your amp in the range of 10% to 60% of its rated power.
@emergingsoul IMO biamping isn't a good option for speakers with difficult impedance curves because it doen't solve the core problem and the complexity increases dramatically. If you use two brands of amps you have to make sure they have the same gain and that the current output into low impedances of each amp is complimentary. If you want to biamp with D'Agostinos or Gryphons then that will work great but things get pretty expensive in a hurry.
