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I recently got the HT-S5305 as it was only £50 more than the HT-S3305 which gets you an active sub (27-150Hz vs 30-150Hz frequency response) and HDMI 1.4a certification. Also someone on AVForums said the following re: HT-S3305 vs HT-S5305
Here are the specs direct from Onkyo for both systems:
HT-S5305: http://www.eu.onkyo.com/ir_img/21833038_e17c7a273b.jpg
HT-S3305: http://www.eu.onkyo.com/ir_img/21918910_3e7c35c34a.jpg
I'm by no means an expert, I'm really just relaying info from others but having owned the HT-S5305 for a week I have got to say it's well worth £300. So far I've watched The Expendables (DTS Master Audio), Star Trek (Pro Logic II), 2012 (Pro Logic II) and Gamer (Pro Logic II) through the system and I was blown away by how good the sound is
Last but not least, if you have a PS3 this guide is really handy for setting up the PS3 to output DTS/Dolby to your Onkyo AVR over HDMI: http://www.avforums.com/forums/onkyo-products/696423-faq-setting-up-ps3-onkyo-amp.html
AVForums said:They are both based on the 308, but the addition of the Active Sub on the 5305 means you have much, much more future proofing. It is easily worth the extra £50 if you can ever see yourself upgrading the speakers.
Here are the specs direct from Onkyo for both systems:
HT-S5305: http://www.eu.onkyo.com/ir_img/21833038_e17c7a273b.jpg
HT-S3305: http://www.eu.onkyo.com/ir_img/21918910_3e7c35c34a.jpg
I'm by no means an expert, I'm really just relaying info from others but having owned the HT-S5305 for a week I have got to say it's well worth £300. So far I've watched The Expendables (DTS Master Audio), Star Trek (Pro Logic II), 2012 (Pro Logic II) and Gamer (Pro Logic II) through the system and I was blown away by how good the sound is

Last but not least, if you have a PS3 this guide is really handy for setting up the PS3 to output DTS/Dolby to your Onkyo AVR over HDMI: http://www.avforums.com/forums/onkyo-products/696423-faq-setting-up-ps3-onkyo-amp.html
for the time being
, figured these will be a nice step up in performance and connectivity