First, your receiver should drive the 703 without any problems and buying a Rotel won't make a blind bit of difference to the sound.
Secondly, good choice to move to the 703; I wasn't at all impressed with the sound of the 704 and 705. The FST driver in the 703 makes quite a large difference as far as I'm concerned.
I owned the HTM7 for a year and sold it after I upgraded to the HTM3S. I didn't like the HTM7 much and thought the sound became muddy once there was a lot going on. It certainly didn't match the FST drivers in my 804S but that was not really very apparent until I switched to the HTM3S - I didn't know what was missing until I changed.
The HTM7 only fully matches the 705 and partially matches the 704. The closest match for the 703 is the HTM3S but unfortunately that center, with stand, actually costs more than a pair of 703! It's been people's biggest gripe about the 703; it's a nice sounding speaker, actually close to the 804S, but there's no matching center for them so they fit stereo applications best.
Keep the money you'd spend on the Rotel and save for the upgrade to the HTM3S.
Ok, so here's what I've decided to do. I'm trading my 704s in for 703s (I have a deal with a local dealer where I get to apply purchase price of 704s towards the 703s so it will be about $800 out of pocket to do so). For now I plan to keep my HTM7 center (I've read on some audio forums that the HTM& may be a mismatch for the 703s despite the fact that B & W sells the HTM7 with all speakers in the 700 series) and see how it goes. I'm also planning to purchase a Rotel 1070 pre-amp to augment driving the 703s (have a Yammy RXV-1700).
Some questions-(yes I'm a noob):
Will I notice the mismatch between the 703s and HTM7 while watching music DVDs (say Dave Mathews Live in Central Park DVD)? How about regular movies - from what I gather if the volume is cranked it might not be that noticeable?
I didn't notice a mismatch between my 704s and the HTM7 and I've read that the HTM7 was designed almost exclusively for the 705s. Do others think the 704s and HTM7 are mismatched too?
Is the Rotel 1070 a suitable pre for the 703s. Will I notice drastic differences in performance with and without the amp? Should I consider another pre amp to drive the 703s. Hoping to spend less than $500.
Do people use a preamp while watching movies via their HTs or is it more of a benefit in a 2 channel set-up? I will use the system for both.
Thanks for taking the time.
Chris