Edit: sorry for the long post, I wasn't aware it would be this long.
Pros and cons of each receiver.
Onkyo pros:
HDMI 1.3 (deep color support)
Dolby TrueHD, Dolby Digital Plus, and DTS-HD audio processing
Powered zone 2
Reputable for ease of use and setup
HDMI upconversion (converts all inputs to HDMI if you wish)
Onkyo Cons:
Reported popping when switching audio automatically (pops slightly through speakers, only a minor annoyance in my opinion)
No multichannel preouts for addition amplification
No scaler
H/K pros:
Scaling (to 720p)
preouts for all channels
pretty hefty at 30 pounds, which indicates it has more power (other receivers in the 25 pounds vacinity)
Looks very nice
HDMI conversion (converts all inputs to HDMI if you wish)
H/K cons:
Not HDMI 1.3, but can still process high resolution uncompressed audio from an HD player that decodes HD audio (Dolby TrueHD, Dolby Digital Plus, and DTS-HD) internally.
H/K's reliability reputation is decreasing (but not as poor as Kenwood, Sony)
Yamaha Pros:
Multichannel preouts
Yamaha cons:
Not HDMI 1.3, but can still process high resolution uncompressed audio from an HD player that decodes HD audio (Dolby TrueHD, Dolby Digital Plus, and DTS-HD) internally.
No HDMI upconversion (can't convert inputs to HDMI)
No scaler
Marantz pros:
Multichannel preouts for adding amplification
Marantz has a good reputation
Marantz cons:
Not HDMI 1.3, but can still process high resolution uncompressed audio from an HD player that decodes HD audio (Dolby TrueHD, Dolby Digital Plus, and DTS-HD) internally.
No HDMI upconversion
No scalers
If I missed something or any of this information is incorrect feel free to correct or add as you wish.
To the OP (Kilim)-
I would recommend starting off with a nice set of stereo bookshelf speakers and a subwoofer. Once you can afford to upgrade again you can get some matching floor standing speakers or another pair of Bookshelf speakers for surrounds, then again when you can afford to add a center channel. This approach will get you the best stereo sound you can afford now and you will have a very nice system once it is said and done with.
The Polk system you mentioned is not worth much consideration, in my opinion. Satellite/subwoofer speaker systems aren't typically that great, and I don't expect that Polk's would be any different. The subwoofer is a really weak point with that system. It won't be able to have the depth and level of output compared to even the most modest separate subwoofers.
This system from BIC (Acoustech) is well received and those speakers can be driven by basically anything. You can find the system online for around $1000, which is an amazing price.
(before it is asked, the H/K's power ratings are considerably lower than their competitors because they rate their receivers with all channels driven at 1khz. The competition does their power ratings with only one or two channels driven in most cases and usually are about the same in terms of power as similarly priced H/K gear.
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