Upgrade capacitors in tube amplifier?

I have upgraded crossovers with very good results.  I now have a "very good" IMO chinese tube amplifier that can probably be improved with a couple of capacitor upgrades.  

I don't have a schematic, but I have a picture and I expect some of you knowledgeable folks can point me to/confirm the ones to change.  My thought is to change the two large silver ones first and then maybe the four smaller silver ones (on the circuit boards). 

Would probably replace with something like Jantzen Superior Z-Cap or comparable and go with a higher voltage if space permits.  



@decooney should weigh in on this one.
Ok i can see the pairs of caps on the circuit boards,, 
Q: are they in power supply, or audio circuit? 
Got to know, Power circuit caps will not result in superior sonics, 
caps in audio circuit, like the 2 on the tube sockets,,will alter sonics. 
If you can geta  solid tech geek to advise, they I suggest go with Munorf Supreme EVO SGO, or EVO SGO.

Really there's not much to work with,,I'd say keep this amp, and later on look at a Cayin, which offers lots of caps/resistors you can swap out. 
On resistors  go with Takman Rey's.
hope that helps

So if you haven’t already done so I would recommend two matched pairs of Tung Sol EL34’s and also upgrade the 12AX7 and 12AU7 vacuum tubes.

I have another thread on the tube angle. Have replaced the 12AU7 and have 12AX7 on order. I’ll study the EL34....these can get into real money.  Edit:  check reveals the Tung-Sol EL-34 are not too bad......but I'll still study the possibilities.

" 1extreme, I realize the circuitry is very different. Generally, do you think there is less potential for a coupling cap upgrade to be as effective as a crossover cap upgrade?"

The answer to that really depends on the other components in your tube amp and the other audio components in your end-to-end audio chain. Do you believe those two coupling caps are really the weakest link in your end-to-end chain? If not then it is unlikely that any improvement would be "revealed" by your system. BUT....this is also about having fun so if getting in there with your soldering iron and swapping components and trying to hear the difference will bring you fun then go for it. Been there and done that, so I’m the last one to poop a fellow audiophiles party.
There are three coupling caps. The first is at the top of the photo, one in each channel. To the far left and right beside the power tubes is a small circuit board; the coupling caps for the output tubes are mounted on that circuit board; they should be matched for best results.