As someone posted before, depending on your use (movies, music, videogames, etc.), room size/conditions, and placement, you might get good performance from bookshelf/sub compared to floorstander/sub. As someone else posted before, you should consider all types of subwoofers and any brands that are available to you. Do not think that you must buy a B&W sub or even a sub from the same product range as the rest of your speakers.
When I was shopping for speakers in late 2003, I was originally looking at 600 series. I compared 602 to 604 and found the difference to be not worth the extra cost. (The 604 had a little more bass, but would still require a sub; so why not buy 602). Then I compared 705 to 602. I preferred the 705 so I bought 705, htm7, and ds7. I did not listen to the 805 at the time. (Too much money and I thought it would need a well treated/designed room to get close to its maximum performance.)
The reason htm7 does not match 703 is b/c 703 is a 3-way speaker using an FST midrange driver whereas the htm7 has no such midrange driver. The htm7 uses a bass/mid driver. From what I can tell on B&W's website, this same htm7 driver is in the 705 and in the 704. Note that I have not listened to 703 so I cannot say that I think it sounds different from htm7. I can say that I have read posts about this before.
Yes, ideally for DVD-A and SACD all five speakers should match and be capable of producing the entire audible frequency spectrum. But few people have the space and money for that. That is why a decent receiver and/or player is important.
By all means, listen for yourself. There are MANY speaker brands out there. Search this website and you can find plenty of names. I have not listened to them but you might want to check Von Schweikert (Audioholics reviewed some of their speakers before), Paradigm, Monitor Audio, etc.
If you haven't already, you might want to check the htguide.com forums. There is a B&W forum there. You might get more responses and can search previous posts but it is a rougher forum than this one.
If you cannot make speaker stands, you might be able to modify existing ones. I use Studiotech stands that I modified to fit 705. B&W stands look nice but they are even more overpriced than their speakers.
