oppmann99,
It's my understanding the pioneer is a bright sounding receiver, and B&W tend to be brighter then the rest.
The general consensus around here is that amplifiers/receivers don't have their own sound. I am in that group, as I haven't been able to distinguish between different makes during any auditions I have experienced. If a mainstream amplifier (Pioneer, Yamaha, Marantz, Onkyo, etc) is not overdriven, you will not hear any differences. Some esoteric "audiophile" makes
might influence the FR - but only if something has been deliberately done to
colourthe sound. And, by "coloured", I mean inaccurate.
So, I wouldn't concern myself too much with the components driving any speakers during a demo, as long as the amp has sufficient power to drive them.
On that note, the B & W's might present a heavier load to an amplifier than the Monitor 9's, so keep that in mind.
If you'll be comparing them, side-by-side, in your home - excellent! I would recommend that you get a friend or family member to assist. It's unlikely that you'll be able to replicate a proper DBT, but you can take some measures to reduce bias during your listening.
Try placing the speakers from both pairs close to each other in their normal placement positions. They'll probably influence the sound of each other, due to diffraction, but they'll be equally handicapped, so I wouldn't be overly concerned by that. You
could have the speaker positions swapped between listening tests - but auditory (if that's the correct word) memory is extremely short. You need to be able to switch between speakers very quickly, in order to make a valid comparison.
You should sit
blindfolded in the listening position, while the other person switches back and forth between each pair ("A" and "B"), at random. Due to the different sensitivities of these two models, he/she should vary the volume between switches, so that you aren't influenced, or at least minimally influenced, by the "louder is better" phenomenon.
I know, it ain't exactly scientific, but at home what else can you do? You've expressed that you aren't completely happy with the 9's, which is fair enough. However, that can subconciously influence your preference during a comparison. The key is not knowing which speakers are playing at any given point during testing.
I'll be the first to say, that the 683's/684's look much nicer than the 9's. I wouldn't want that to influence judgement of the sound quality of each speaker. Unless, of course, the appearance of your speakers is important to you. That would put a whole different spin on the situation....