As I am considering buying a new receiver, I have been examining both of these models closely, and I thought that I would share my findings as well as ask for any other people's opinions. Note that although the 5ES is discontinued in the U.S., it is still very much a currently available product in Canada (where I live). Both receivers have: [*]Dolby Digital EX (see below for note on 5ES)[*]Dolby Prologic II[*]DTS-ES Discrete 6.1[*]DTS-ES Matrix 6.1[*]DTS Neo:6[*]Component Video Switching with High Definition pass-through[*]5.1 and 7.1 Multichannel Inputs[*]32 bit x 3 DSPs[*]96k/24 bit PCM capability[*]On-Screen Display[*]Digital Cinema Sound[*]6.1 Channel Decoding[*]Virtual 6.1 playback capability[*]Analog Direct and Analog Pureness Controls[*]18 Digital Signal processing modes[*]Digital Cinema Sound Cinema[*]Studio EX A/B/C modes[*]Equaliser with 5 presets[*]Tone control (in addtion to EQ) in many soundfields[*]SoundField Link[*]Front Audio/Video input[*]Screw type speaker terminals[*]Gold Plated Headphone Jack[*]S-Link (Control A1-II & Control-S)[*]RS-232 port for upgrades and system control[*]Sleep Timer[*]Detachable Power Cord[/list] The 4ES exclusively has: [*]DTS 96/24[*]genuine Dolby Digital EX decoding[*]2 Zone/2 Room capability (2nd A/V out) with E. Volume[*]Speaker A/B switch[*]Composite to S-Video Up Conversion[*]Pre-Programmed (one-way) LCD Remote with Macro[*]110x7 power output rating[*]Equaliser: (B=Bass, M=Mid, T=Treble) [*] Front (B,M,T) [*] Centre (B,M,T)[*] Surround (B,T)[*] Surr.Back (B,T)[/list][*]Two 12 V triggers (one per zone)[*]IR Repeater input (1) and outputs (2)[/list] The 5ES exclusively has: [*]3 Zone/3 Room capability (2nd A/V out, 3rd speaker out)[*]Pre-Programmed (two-way) LCD Remote with Macro[*]Additional remote for 2nd or 3rd zone[*]110x6 power output rating[*]Equaliser: [*] Front (B,M,T) [*] Centre (B,M,T)[*] Surround (B,T)[*] Surr.Back (B,T)[/list][/list] I am leaning toward the 4ES for a few reasons: [*]I will be using two Surround Back speakers. The 4ES has built-in amplification for two (independant) Surround Back speakers. The 5ES has only 1 channel of amplification, but it has two independant pre-outs so that an external amp can be used to achieve a 7.1 setup.[*]the IR repeater functionality of the 4ES is something that I will actually use[*]...as is the 12 V trigger.[*]Although the 5ES comes with a 2-way remote and the 4ES does not, the 4ES has the capability to use one. I already own one that I plan to use with it (knowing that some of the 4ES' setup parameters will not be accessible using it).[*]The 4ES has A/B speaker hookups. I will use this.[*]The 4ES has genuine "Dolby Digital EX" decoding. The 5ES will decode the extended surround channel of DD-EX material, but it does not have a genuine Dolby decoder. It uses Sony's DCMD (Digital Cinema Matrix Decoder) for DD-EX material. The 4ES can use either Sony's DCMD or Dolby's decoder. Both have genuine dts-ES (discrete and matrix) using dts' or Sony's decoder.[*]The 4ES has dts 96/24.[*]According to the specs (as posted on the sonystyle.ca website), it 3 kg (6.6 lb) heavier than the 5ES. (4ES: 20.0 kg, 5ES: 17.0 kg). This probably indicates a significantly heavier power transformer (provided that the specs are correct).[/list] The 5ES has these features that I wish the 4ES had too: [*]3rd zone amplified output. I could really use this, and it is the one feature that is most pulling me in the direction of the 5ES.[*]2-way remote and a second remote for another zone.[*]better/bigger capacitors in the power supply (rumoured)[*]an 'absolute position' type volume control. The 4ES has one of those continuously-rotating jog-dial types. Both are, ultimately, fully electronic (not actual analog pots).[/list] I had been wavering, but upon finding out that the 5ES does not do 'real' DD-EX and does not have as good of an EQ (in the surround channels), I have really swayed over to the 4ES. The 5ES currently retails for CAN$100 more than the 4ES (equal to about USD$64 more). Does anyone have anything else to offer?