Integrated for B&W PM1

Here's my story, and it's a head-scratcher, but it is what it is, and I could use some input...

In my 12x10 listening room I have a pair of B&W PM1 connected to a Marantz PM8400. I bought them at the same time, they sounded good, that was that.

Our living room 5.1 system centers around a pair of Mirage OM-9 bipole towers running off a 2003 Onkyo TSX-R701 100wpc receiver. The living room setup is just for movies and casual loud music while cleaning the house, and it sounds good and the Onkyo and Mirage work well together (much better than the SF Grand Pianos which were a lousy match with the Onkyo, as you'd expect). The OM-9 aren't speakers you use for critical listening, in my opinion, because of the bi-pole sound, but I'm a big fan of the way they can fill a room as if you have much larger speakers, a very cool enveloping effect.

So this past weekend my gal asked me what the PM1 would sound like compared to the big Mirage towers, so I dragged them into the living room for the first time just for kicks. And we were shocked by what we heard - the PM1 sounded worlds better than they ever sounded on the Marantz. It was like they opened up and just completely filled the room with this amazing 3-dimensional wall of sound; it was like a wall of vocals, in front of a wall of percussion, in front of a wall of strings. Even the bass performance was incredible - not quite the equal of the OM-9 (which have multiple forward and rear firing bass drivers), but it was much closer than I expected. And of course, the mids and highs of the PM1 were much better than the OM-9, which was not a surprise. I actually got goosebumps, it sounded so good.

To make sure we weren't just hearing the difference in room acoustics, we dragged the Marantz into the living room and did an A-B comparison, and we weren't imagining the difference. The Marantz just could not keep up, and it was like someone threw a towel over the speakers.

Hence, the head-scratcher. I just can't understand a 10-year old $500 Onkyo making $2800 PM1s sound better than a $1000 Marantz. There is an output difference, 100wpc to 70wpc on the Marantz, but can that be the reason for such a dramatic performance difference (volume levels being equal)?

And now, where do I go from here? I haven't even hooked the Marantz back up now that I've heard what the PM1s CAN sound like. Do I hit eBay and buy a used $150 Onkyo? Or should I expect that if I go back to a nice integrated, I'm correct in assuming that I should be able to improve on the Onkyo? I've been reading up on the W4S STI-500, or maybe the Bel Cando S300iu, something with a lot of power. Or even a Rogue Sphinx. I don't mind dropping $1500 on something, but if it ends up sounding no better than a 10-year old Onkyo I'm going to bang my head on the wall!