I recommend you do some research on avsforum.com. There is alot of info about the comparisons you ask about.
When a dealer gave me a brochure about the 59, I got excited and started checking it out. Unfortunately, as soon as I started investigating, it sounds like neither the video nor the audio sections have progressed as far beyond the 47 as I had hoped, though the HDMI connection is a big advantage.
HDMI (with copy protection) will 'probably' become the new standard for audio & video data transfer in the pure digital domain for the next generation of AV equipment. But, until there are HT pre/pros with HDMI switching, this is only going to benefit the video display unless you intend to use the TV's speakers themselves (I could care less if I even HAVE speakers in my next TV!).
From many of the reviews I have read, Pioneers uni-players typically have poor SACD sound and the old PureCinema technology still in use is known for video artifact issues and is generally considered inferior to the Faroudja processing chips. (NOTE: There are several different levels of Faroudja chips. I believe the 'Stingray' chipset is still their most advanced version - used in some of the most expensive SOTA DVD players.)
Also remember that the Denon 5900 (and a few others) has DVI outputs, which is compatible with HDMI connections, though it only carries Video signals in pure digital form - not audio.
Disclaimer - NO insult is intended here - If you have a 59 and love it, then you have found the magic for you - FEEL LUCKY & ENJOY!!