Help in building a KEF surround system

I would like some input on a KEF surround system I am currently building.
Right now I have 4 KEF 104.2 speakers,two of which I am the original owner.
I want to to build a 7.1 system.I have the marantz mm8003 and will be soon buying the av8003.
My questions are:
I can use the 104.2s for the sides and rear with the thought that I have an opportunity to buy some 105/3s that I can use for right and left fronts.
Would these match sound wise? Should I buy two more 104.2s for the right and left fronts and stay with that? If not what would you recommend for the right and lefts?
Lastly what center channel would you recommend? I have read that the 200c is a good match but good luck finding one.I do want everything to match sound wise so your input would be well appreciated.
I also have but have not built yet 2 Dayton RSS390HF-4 15" Reference HF Subwoofers with 2 1000 watt amps.
Thanks for your help!!
the conventional wisdom is to match your speakers as closely as possible in a surround set-up--ideally you should use seven identical speakers. aesthetics aside,then, you'd probably get the most seamless sound from seven 104.2s; alternatively use three pairs and then find a kef from the same vintage to use as a rear center, which is probably the least critical.
Thank you for your help.

As far as a center channel goes...any other recommendations?
I talked to KEF USA and was told the IQ60c would be a good match.Does anybody have an opinion on that?
Perhaps i will get lucky and find a 200c for sale soon.
Are you planning to use this system mostly for home theater use (movies), or mostly for multichannel music (SACD or DVD-A)?

Assuming the former, I think KEF 104.2's would be gross overkill as side/rear surround speakers, and they may actually be poor choices for at least three reasons: 1) They need at least 6 feet, preferably 8 feet or more, to sound their best -- do you have that much distance between all listening positions and the side/rear speaker locations? 2) The side/rear speakers are frequently mounted a few feet above ear level -- this would be difficult with the large, heavy 104.2's. 3) The 104.2's like to be powered by plenty of clean, high quality watts, which the Marantz receiver may be unable to deliver, especially if it is the sole source of power to all 7 speakers.

I have been very happy with my 104.2's as front main speakers for 21 years. I have used a 100C for the center channel for 15 years. Although others will say the 200C is a better match, I have been perfectly happy (except for some age-related deterioration at age 12 that I repaired myself) with the 100C, at less than half the cost of the 200C.

I use a pair of KEF Q2ds, mounted on the walls a few feet above ear level, for the side surrounds. They sound fine, but I was disappointed by their fake woodgrain finish, which the IQ60c uses as well. If your center channel speaker will be in a visible location, then you want it to be as attractive as the 104.2's with their real wood veneer.

I use a pair of Paradigm Titans, mounted on stands slightly above ear level, for the rear surrounds. They have been trouble-free for 15 years.

I believe that the "conventional wisdom" of using identical speakers in all surround locations is overrated and unnecessary for home theater applications, now that the receiver/processor automatically calibrates the volume of all speakers, and frequently does room correction on them as well. I suggest that you get some small speakers for the side/rear surrounds, either vintage KEF 102.2 if you want to stay with KEF and can find them, or any decent bookshelf or wall-mountable speakers from a reputable manufacturer for no more than a few hundred dollars per pair. For the front center channel, I suspect that most dedicated center channel speakers, costing no more than a few hundred dollars, from any reputable manufacturer, will be a good match with the 104.2's.

I personally like dipole speakers for the side surrounds and monopoles in the rear, but others prefer monopoles in all locations.

P.S. -- Hurry up and build those subs! Enjoy.

Thank you Java and others for you feedback.At some point I will be doing an addition the my house and would design a room large enough to accommodate the 104.2s.But now you got me rethinking everything as I have no experience at all using a surround system.I might play at first with my 104.2s as is in my smaller room to see what I hear etc.If the sides and rear channels do not put out any so to speak 20-20000 "full range" material as the center and left and rights would then it would be overkill.If the sides and rear are just simply "fill" then you are for sure right.Does the center channel usually have "full range" material going to them sound wise?
If so then I will invest well in those.
I really appreciate everyone's feedback so far.
Got me to thinking!!! again!! lol