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.  



The amp is a Willsenton 35i.  Around $88o including air shipping from china hi-fi.  I'm really impressed by it.
After looking at the Willsenton web site I see that they use generic EL34 tubes stamped with their Willsenton name. (I'm sure Willsenton is not manufacturing tubes.) At that price point they are likely not higher quality tubes. Even expensive tube amp manufacturers often use "budget" tubes expecting the buyer will roll them to higher quality tubes.

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.
If you do upgrade just do the coupling caps connected to the tube sockets and realize a speaker crossover environment is very different from a tube amp.
1extreme119, 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?
@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