Help me plan my next upgrade

I'm making the jump from the Onkyo 989 receiver to separates. I just bought an Arcam AV8 here on Audiogon, and will likely close on an ATI 2007 amp this week. My 3 front speakers are M&K 150THX, the sub is M&K, and the 2 rears and 2 surrounds are in ceiling B&W speakers. I haven't yet purchased any of the cabling. The DVD play is the Denon 2900. The TV is a Toshiba 52 inch.

Where would be the biggest bang for my buck for my next upgrade?

Thanks in advance for your response.
1) Plasma TV?
2) Replacement of in-wall speakers with true conventional speakers?
3) Dual HSU or SVS powered subs?
4) Progressive DVD player?
5) Power conditioner?
I don't know your budget, and I'm assuming that your pref. is 50% HT & 50% music (possibly DVD concert).
A front projector..if you have the room.

Lots of good suggestions so far. I'd like to add cabling, especially power cords now that you'll have a real amp. Perhaps Shunyata matching (1 pacesetter/1 noise reduction) cords or Synergistic Research. Now that you're changing the sound of your system dramatically, I believe that you try to help each component be the best it can be.
Dedicated line and good cheap Power Cords (disclaimer, yada yada yada). RSVP. Ern
Power conditioners make a world of difference in every aspect of a home theatre. They improve color and clairty on televisions of every type, and improve sonic performance like no other add-on peice of equipment can.

Monster makes the most affordable units and the HTS 5100 Signature series would be a definite asset to your system.

As for cabling, not all cables are created equal. Technology does matter. However I have found that once you get to 100-400 a meter for interconnects they are built well and have a considerable amount of technology for the guy that cant spend 10K on cables.

I too had the DS989. I made the jump to Bryston Separates SP1.7 Processor and five 7B SST amplifiers.

Best of luck on your search for Audio Nirvana
2-piece projection either front or rear. For an immersive home theater experience you want to be sitting arround 1.5 screen widths. At normal living room seating distances (beyond 9 feet) this isn't possible with the largest one-piece consumer televisions (~ 80" diagonal rear projection).