What are you using for a source for 2 channel? If digital, you need to compare the DACs in the 2 receivers. If analog, there should be less of a difference in the two. But, an external power amp will probably make more difference than the DACs, depending on the speakers.
Which Would You Choose?
All other things being equal, which of these two options would you choose? The goal is quality 2 channel listening with the ability to have a solid home theater experience. 5.1 surround sound is more than adequate with the primary focus being put on the mains.
Option 1
Marantz SR6006 - $1,200
110 wpc (x7) AVR
Option 2
Marantz NR1402 - $400
50 wpc (x5) AVR with 2.1 pre-outs
AND
Marantz MM7025 - $800
140 wpc stereo power amplifier
Would the power amplifier be expected to be a significant improvement in stereo sound quality?
Option 1
Marantz SR6006 - $1,200
110 wpc (x7) AVR
Option 2
Marantz NR1402 - $400
50 wpc (x5) AVR with 2.1 pre-outs
AND
Marantz MM7025 - $800
140 wpc stereo power amplifier
Would the power amplifier be expected to be a significant improvement in stereo sound quality?