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.  



I'd be careful about anything that is paper and oil in a tube circuit. Over time its not that unusual for them to develop a bit of electrical leakage; this can throw off the bias and operating points in the circuit.

FWIW we've had good luck with the V-Cap ODAM series in amps like this. That part also appears to have an oil component, but it doesn't appear to have a paper component. At any rate they sound pretty nice and we've not had any problems with them.
I really like the internal wiring on that tube amp. Very neat and organized. 80% point-to-point except with the few pcb boards and thicker wire than a lot of more expensive domestic amps.

My thoughts on the cap upgrades is to not do it unless you hear something you think is deficient and you have already upgraded the tubes and interconnect cables.

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. Make sure the capacitors are rated for higher temperatures as well as higher voltage.

What make is that tube amp?
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.