I compared Philips, Sony DZ610 and LG HT-924 as I am also looking for a simple 5.1 system for around 20k which I can shift to my bedroom. Had demos on all 3 systems and I found the HT 924 from LG sounding the best. Bass was nice, interface was good, it had HDMI out, Monitor out, Component Out and Optical In. So if I want to attach a WDTV HD Media Player to this system for the sound through the optical out, it is possible.
The Sony models cost more but aren't really better sounding, though they do look better.
At E-Zone here in Chennai today, the LG HT 924 was on offer for 14k while the Sony systems were starting at above 14k. So the DZ510 and 610 may cost around 19-20k. I compared the LG and Philips systems today (Philips 600W RMS, LG 1200W RMS) and the LG sounded way better.
Last week I had compared the LG HT 924 with a Sony DZ610 I think, and the Sony had excellent bass, but overall it sounded boomy. The LG had better sound quality overall with decent bass, being a passive subwoofer.
For the price, the LG HT 924 seems really nice, as it has a USB port and you can record directly to MP3 on USB from CD and FM.
If you can spend upto 25k, then you may as well get the Onkyo HT-S3300 which is much more powerful and future-proof. If you don't like the satellite speakers and passive subwoofer, you can always upgrade to better speakers and an active powered subwoofer after some time, as the receiver supports the same. This model has been purchased by one of our forum members in Coimbatore for 23k which is phenomenal value!
---Venkat