OK, I'm one of those annoying guys who says that if you didn't listen blind, your ears were most likely overwhelmed by your eyes. (Or the "high end" amps were tube amps.) Your speakers are rated at 90dB sensitivity and 8 ohms, which should be an easy drive for any properly functioning solid-state amp. (Or it's also possible that the Denon is not properly functioning, though that seems unlikely.)
The Lyngdorf should be completely fine for driving 90dB speakers in a 25sq.m room. I have 89dB speakers in a 30sq.m room, and have no problems. But if you can buy it with return priveleges, that would be the way to go.
The mini-DSP SHD may also fit your needs, though it appears to be much less user-friendly, per the soundstage review. I went with Lyngdorf over mini-DSP because of its user friendliness, and because Lyngdorf supports Apple Airplay.
The one thing I know for sure is that I will always consider room correction to be an absolute necessity for any system intended for anything more than casual background listening.