Capacitor

The Miflex caps offer great performance for the price. They are modeled on the Duelund caps which are insanely expensive.

Obligatto caps also offer great performance for the price. 
Used both brands when recapping my tube amp and have also used in other applications.

Miflex has served me very well.

As far as changing values, that is fully dependent on the circuit design…

@grannyring
I received a mail from canary the 3uf caps are signal caps so will a lower value be ok

@bpoletti 

Changing even a single component ( pairs in this case - left+right channel) can, and does, make a huge difference in sound. In many cases more so than going from bad speaker cable to good ones.

There is no "design flaw". A good analogy would be a motor car getting a new, and much better, tires. The car is still the same, but a good set of tires can increase mileage, shorten brake distance, improve handling and make the vehicle safer. Same for an amp. It still the same great amp as before but it's a little enhanced, a little improved.

It costs a couple of $100 to upgrade caps vs. the tens of thousands new pre - amps will cost. New pre-amps, which incidentally will have the same or similar mediocre capacitors we are replacing in the Canary pre amps; meaning we'll be back at square one looking to upgrade capacitors in our new pre amps.

If by signal he means they are on the RCA outputs, then yes you can change. Don’t change the value of interstage coupling caps. 

@pauly
You are absolutely correct there is a brand I do not want to name he has 3 line stage the basic, enhanced and super enhanced and the only difference is the parts used but the price is almost 40% more in each step up