Need help on center speaker to match with my front

Another Index will work great, get 3-4 more and do the whole surround system in indexes.

That would be ideal

Thanks for your response!

OK I am new here and I have few problems:
just got my NAD T753 (Linn Index in the front, Linn Afekt sub, Linn Unik center, Denon surround sound) - I know not a perfect setup, but I am in the process of upgrading.
1. Why do we need to buy expensive "full range speakers" when we are going to set the subwoofer to take care of all of the frequency below 60/80 Hz? This is not making sense to me... any help please? I believe a good sub with cheap speakers will do the job as well. What am I doing wrong?
2. The NAD T753 does have the hush noise and it is noticeable... I have also an old (10+ years) NAD 302 integrated amplifier and the sound is much better compared to the T753. Is this the end of the NAD era?

Thanks for you response! So I guess the solution is to use my old NAD 302 integrated amp with my Linn Index speakers for listening to music (NAD 502 cd player), and setup the NAD T753 receiver for home theater using the Linn Afekt sub and 6 low priced/not full range speakers - for example 6 Linn Unik ($225 a piece). It does not make sense to buy good/full range speakers for home theater and then to send all the low frequency to the sub. I think this should be my target - I just need to find 5 more Linn Unik (have one already) and I should be good to go.
Thanks!