"What should I check first?" First you should check who is able to help you there with instruments and experience.  I'm not writing this to discourage you, I want you to able to complete the mod. My ability to help is limited from here.

z5500 digital "Which option is correct?" The few old photos I have is useless, no Z amplifier board around to check. "Are there any errors in my scheme?" If you connected all the pins marked with X together in the square, that should work.   Bagheera "Is all of this correct?" Correct, but...

Few ideas: Perhaps you can check the sound from the Pod with a headphone. If the OpAmps not getting what they need under the load, probably you gent no sound directly from the Pod. Because circuits in the Pod powered from 2 different sources. The +18V -18V is for the 11 OpAmps, the +8V is for...

"Should there be contact on the PCB between the terminal for filter capacitors 10000uF (between minus C29 and Plus C30 )" Yes.

"But wonder if it can burn both R21 and R22 resistor." When the filter capacitors have a bad contact you get hum, but If it was a hot ground problem..... I just do not know how the regulators behave without it. "K73-16 0.22uF 160V is it ok?" It is.

Obviously short circuit. Can be small, hard to detect. Or misplaced mica insulator(s), solder drop, metal fragment, screw between the pins of the TDA AMP. Component installed the wrong way, left out, damaged, bad solder joint. Long list of possibilities.... If you find the mistake, you may...

Listed on the first page.

Yes, that's what I mean. All you need is in the "Third Mod".

Not that hard: http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=k73-16+0.47uF&LH_PrefLoc=2&_sop=15 Get the 71V Kenwood, the 75V is too fat. Denon is the best you can get.

The WIMA MKP certainly do the job, but you may find the bigger axial films more transparent sounding. I was using K73-16 and K73-11 63V in this positions from eBay.

I think 4pcs OPA1602AID all you need for the Audigy RX. Inside the Sub: Use a pair OPA1602AID for the Sub woofer. The rest can be 3pcs OPA1602AID, or better if you use 5pcs 0.47uF film capacitors. Inside the Pod: Use 6pcs OPA1602AID.

Use a multi meter. Probably you will not find +18V and -18V on the D-Sub pins because one or both of 78M18 and 79M18 regulators are dead, or maybe one electrolyte cap failed in short near by. Or damaged trough hole current limiter resistor beside. If you are really short on luck, there are few...

Just by looking the pictures you obviously work like a pro, and know what to use for the job. I spotted some differences what I have never tried, and maybe the source of the problem. I had only the two main filters on wires in the first mod and still in that way years later, and giving no...

Thoughts: If the soldering is checked OK by instrument, no pad is missing, if the board was not removed probably some SMD component got too much heat. Or there is a drop or fragment of solder somewhere. Or while using a good old fashioned soldering gun the current flown on an unexpected path on...

"COMPLETELY bypasses all the DSP" Then it was the right choice indeed. You won't get the same pure sound from your old amp just by swapping components, too much stuff on the signal path. Even a cheap pot alone butcher the sound, nothing to say about the rest what is usually stuffed in an...