By av cables do you mean the hdmi cable from the ps3 /skyhd to TV?
Well you can spend less than £10 or a kings ransom on a HDMI cable. So depending on distance, i would start cheap and work my way from there if need be.
For instance, i paid £30 (was £50) on this: QED Classic HDMI-P Cable 1m 2 years ago and a while later also bought 2 of these Linx Platinum Pro Hdmi Cable / 10.2Gbps / 1.5m from Play.
I don't have a big LCD or Plasma yet but on my 23" LCD tv i can't tell any difference between them. if the distance is 10m or more i would spend substancially more, but for 1-5 meters there isn't much or any difference in picture quality between the expensive and cheap brands. If the cable is very cheaply made with little or next to nothing sheiding, then problems can arise
All sites that i have linked to have a range of cables from the very cheap to the very expensive but Futureshop and Audiovisual have more of an extensive range. The lesser known brands names will charge less for the same cable which the bigger names are charging 3 or 4x the price for. However they come into their own when the hdmi cable is over a much greater distance (10m +)
If in the future you think the sound can be bettered then you can spend more on cables but the ones above are good enough to get you going.
Looking for a smaller system to replace the aging Hitachi Opus 2 that is currently making my bedroom system, and I looked online and this caught my eye, does anyone have any experiance with them and if so are they any good?