Peng, I totally get what you're saying now. I had no idea that my 4300h & the 3500h had identical DAC n preamp. I'm going to focus on finding another dedicated amp for the other 6 channels and use my AVR-X4300h solely as preamp processor and see how that goes. I'm looking at the Outlaw Audio 7000x 7-channel amp. Price is very reasonable. I would love the Monolith 7x but its a grand more.
The X4300H, X4400H, X4500H, X3500H, X3600H, SR6011, 6012, 6013, 7012, 7013, 6014, and even the SR8012 and AV7705, all have the same preamp vol control IC and DAC IC. The AV8805 and AVR-X8500H do have a better DAC, but still the same preamp vol control IC.
Regarding adding another amp, the Outlaw 5000 did not do any better in their THD+N, IMD, SNR and DR measurements. Reality is, people may think if it costs more, and is a "dedicated" component, it must "sound better" than AVRs that have everything jammed in one box, but that's not always the case, far from it. I compared a X3500H side by side with my separates, at low spl I heard no "better sound quality" whatsoever, but of course that's just me, though bench test results seem to support my own comparison listening subjective impression.
More expensive separates do typically offer better build quality, and likely better reliability as well. They also tend to look better, and may have a better feel to the touch too.
If your X4300H is driving a 5 channel amp for the L,C,R, you could just continue to use the internal amps to power the surround and height/Atmos channels. Adding the Outlaw 7000 won't get you any better sound quality, but it may make your AVR run slightly cooler. A couple of the quiet (at low speed) usb AC infinity fans for about $20 may be a much better value than the outlaw 7000, and may actually do more in contributing to longevity.
Back to the objective side, you can see from the chart below that the Outlaw 5000 amp currently ranks below the X3500H in the ASR reviews. You can safety assume it would rank below the X4300H too. The Outlaw 7000 would most likely perform about the same as the 5000, it has two additional amps and its rated output is slightly higher, that's about it.
This is a review and detailed measurements of the Denon AVR-X8500H Flagship 13.2 Audio/Video Receiver (AVR). It is kindly loaned to me by a member and costs US $3999. The 8500H is a beast: it is both deep and heavy. Thankfully the transformer is centrally located so as manageable as 51...
www.audiosciencereview.com
By the way, in case you may not be aware, since you are running 7.1.4, make sure you use the amp assign function to disconnect the internal amps. Once you do that, the pre-outs will be able to maintain >95 dB SINAD up to 2 V or higher. This is important if you are using a high power amp especially one that has below average gain, say less than 28 dB. The AV7705 only managed about 75 dB at 4 V, XLR, or 2 V RCA, so the X4300H can do quite a bit better. For measurements, just refer to the ASR tests on the AVR-X3600H and AVR-X4700H as those were measured with the internal amps disconnected.
Note: The AVR-X4300H through X4500H and SR6011 through SR7013 do not have preamp mode, the amp assign feature only let you disconnect the front left and front right channels.
