First let us clear your PS. If you don't like the Marantz, you will certainly not like the Azur 640R. The Azur has been made to be a musical amplifier and gives equal importance to both music ad movies, and because of the CA background, leans more towards music.
I think ultimately you have to choose between Yamaha and Onkyo. But here you have made my job very difficult. You want me to choose from 4 very good receivers? Give me a break !!
In the Yamaha, though it has less power, the 863 seems to have more features such as Dolby Digital EX, Neural Sound, HD Radio, DTS Neo, and Bluetooth compatibility. The 1800 does not provide anything greatly esciting to justify its additional price.
In Onkyo, it is much more difficult. The main difference is power. Other wise both are very capable amps.
So we have eliminated the 1800. You have to choose between the 863, the 805, and the 705. A lot also depends upon the budget. If you can afford it, I would go for the Onkyo 805. On a more budgetary scale, you have to choose between the 705 and the 863. The 863 is not THX Certified, and that is an advantage the 705 has. Other than this both have superb sound processing capabilities.
What I am going to do is to help you in your choice by showing you some professional reviews. Read them and then we will see which one you want. Each is followed by a paragraph of conclusions. If this helps you decide, please do let me know what factors you used to decide.
Yamaha 863
Home Theater: Yamaha RX-V863 A/V Receiver
Yamaha has long excelled in the $999 receiver category, and the RX-V863 is no exception. This receiver has a smart new feature set that combines original ideas (scene), rarities (Bluetooth), and new things we must all have (Dolby TrueHD, et al.). The graphic user interface could use an overhaul, but apart from that, this receiver is right up to date.
Yamaha RX-V863 7.2 Channel Home Theater Receiver Review & Information
For about $1,000, you get an awful lot of features and performance with the Yamaha V863. Don??t be put off by its modest looks, as the V863 sounds every bit as good as its similarly-priced rivals and even better than some home theater receivers costing twice as much. It??s a good value and a terrific receiver, highly recommended.
Onkyo 805
Onkyo TX-SR805 Multi-channel Home Theater Receiver Review & Information
For close to $1,000, the Onkyo 805 is one of my favorite receivers available today. Sure, it doesn??t up-convert everything to 1080p, but that??s about all it lacks in terms of features when stacking it up against the competition. However, that little ??cheat? so many enthusiasts like to spew out at you will cost you more and, if you already have the HD sources like a Blu-ray, HD DVD or DVR player, then save your money and rest assured that the Onkyo 805 is probably all the receiver you??re going to need for a long time.
Onkyo TX-SR805 AV Receiver Review — Reviews and News from Audioholics
The design approach applied to the TX-SR805 is clearly geared more for audio performance. All of the audio processing is cutting edge and the amplifier section walks all over the competition. Video processing is adequate, but is not by any stretch cutting edge. As I previously stated, if one wants or needs the additional video performance, the TX-SR875 is looks to be everything that the TX-SR805 is with the addition of HQV 1080p video processing.
The good news with the TX-SR805, while the video processing is limited, it conforms to the latest enhancements that HDMI 1.3a offers, so it will not bottleneck system performance as 1080p and high bit Deep Color become the norm.
Based purely on audio quality of the receiver itself, the TX-SR805 will easily compete with any offering at or near its price. With lossless decoding and Audyssey engaged, nothing comparably priced that does not include HD audio or Audyssey will even come close.
Onkyo has clearly upped the ante with the TX-SR805. With the level of audio performance, HD audio decoding, high build quality, THX Ultra2 certification, and the myriad of cutting edge features, the TX-SR805 is highly recommended.
Onkyo TX-SR805 Receiver�-�AVRev.com
With a retail price of $999, the Onkyo TX-SR805 is a juggernaut. How Onkyo is able to pack so much performance, technology and livability into such an inexpensive package is beyond me. A year ago, a receiver boasting half of what the Onkyo TX-SR805 delivers would have run you twice as much, which speaks not only to the sheer value of the TX-SR805, but also to the efficiency and prowess of the Onkyo designers themselves.
The TX-SR805 does so many things right technologically, and sounds more high-end than any other receiver I??ve heard in recent memory, that I have no inclination to remove it from my rack any time soon. As bowled over as I was with the Yamaha RX-V861, nothing could??ve prepared me for the TX-SR805. Don??t get me wrong, there are other great receivers out there, but it??s the completeness of the TX-SR805 that astounds me most. Be it music or movies, high definition or standard definition, adding or subtracting gear or even operating another zone, the Onkyo TX-SR805 simply shines. It is the first feature-packed receiver I??ve encountered that doesn??t appear to be preoccupied with its own technology. Instead, the TX-SR805 opts to entertain and, while the latest technology may play a role in the total enjoyment of your system, tearing your hair out to get to it isn??t entertaining. The Onkyo TX-SR805 is a wonderful receiver, one Onkyo should be proud of and one you??d be silly to pass up.
Home Theater: B&W 600 Series Speaker System and Onkyo TX-SR805 A/V Receiver
Both B&W and Onkyo (and many other manufacturers) offer higher-end products that presumably do all the same stuff and do it better. In a direct comparison, I??d probably notice the difference. But if I never got another set of review samples, I??d happily live with this system forever.
Cheers