Personally, I would not use the home cinema-in-a-box system for this tv as it would not be doing it justice. You may well still want to go for the deal and just use the cinema-in-a-box for a bedroom tv maybe? To make the most out of the superb Panasonic PZ81, I would use it in conjunction with a proper home cinema amp compatible with the high-def audio formats (to match the high-def visuals from your PS3) - Dolby Digital Plus, Dolby True HD, DTS-HD, etc. One amp compatible with these new sound formats is the excellent Onkyo TX-SR606, for just £399. As for speakers, the Q-acoustics 1010i 5.1 system (£499 or less) is a great match. Of course there are many other high-def amps and speakers, but the Onkyo / Q-acoustics combination is a particularly superb one and at a very reasonable price.
To get HD audio from the PS3 you will need to plug the PS3 into the Onkyo with an HDMI cable, then plug the Onkyo into the PZ81 with another HDMI. You should also plug the Sky HD into the Onkyo with an HDMI (although unfortunately Sky HD doesn't currently support any of the high-def audio formats - only Dolby Digital, but it will still sound great!) and Wii into the amp via component / optical or coaxial for digital 5.1 sound) - taking into consideration the HDness of the 360 and the HDlessness (but still progressive-scan) of the Wii. Because (I think) VGA is the only way to get a full 1080p feed out of a 360 without an HDMI port, you should probably use a VGA connection which probably won't be on the amp so you should plug the 360 directly into your PZ81 and connect it to the amp for digital audio with an optical or coaxial lead, which is fine as the 360 does not support HD-audio, only Dolby Digital 5.1. You could also just plug the 360 into one the amp's component inputs (alongside the Wii - the amp has 3 component inputs!) for a great 1080i picture and again use either optical or coaxial for pumping your digital 5.1 audio into the amp.
This is just my advice, but if you decide to do this then you will end up with an absolutely stunning home cinema system and you will be seriously pleased with yourself, and will be satisfyingly future-proof for a long time yet!