I've used a variety of amps over the last 40 years or so and haven't had this experience, and I would think if anything was coloring the sound it would be your avr as pre-amp. I've used amps of a wide variety, of much higher output than 140W into 4 ohm, too (my primary avr does better than 240 at 4 ohm to boot; my power amps much more than that).