The Onkyo TX-DS595 is basically the 575x with more power and DPL II. Check out this comparison: http://www.onkyousa.com/model_compare_show.cfm?class=receivers&m=TX-DS595&compmodel=TX-DS575x
When I bought my receiver last year, I listend to practically all the mainstream brands available in Manila for below PhP100k.
The one I liked best was the EAD Theater Master and it's matching Powermaster amp. But my budget HATED that combination.
My favorite for HT is Yamaha. Even just the 595a had tremendous effects steering and good enough power. I later learned that inside the 595a's processing circuits is the revered DSP-A1. But I didn't go with any of the YAmies due to stereo performance: soundstage was flat, presentation was rather brittle.
To my ears, the Denons (2800, 3300, AVC-A1) and the Onkyos (575x through 777) had comparable HT and Stereo performance with the only differences being on sound character: the Onkyo was warmer and the Denon was more detailed. I also found the Denon's soundstage to be more obvious (note, I'm not necessarily saying the Denon soundstage presentation is better). My personal preference between the two is Onkyo since its warmer presentation tend to benefit entry-level speakers typically used with models like the 575x. My brother-in-law matched it with B&W DM302/CC3 and the system is glorious! We auditioned the Onkyos with PSB Alpha and Acoustic Energy and the results were great, too.
I guess between the Denon and Onkyo, the choice would depend on your choice of speakers.
I also liked the Rotel RSX-975 (I'm not usre of the model anymore) but held back due to reliability issues raised on some magazines and on-line forums.
My money went to the NAD T760. Soundstage had less width than Denon but had more accurate placement. The NAD has the Onkyo's warmth (even more) and better real world power. The tuner section on the NAD is a decent bonus. Some people hate the minimalist features (only surround modes are DD, DTS, stereo, and proprietary EARS) but that's exactly what I like!