Properly designed amplifiers, any class, will be sure to manage the internal heat such that the capacitors see the least heat;
In the case of modern Class A or AB amps of 30 watts or more, the semiconductors are interfaced tightly to large heatsinks. The thermal path is then (predominantly) convection up through the heatsinks into open air; Some heat will thermally conduct along the PCB ground plane (if there is one), power supply wires, traces and bleed into other components;
The power transformer will heat up as well, becoming a radiator of heat inside the chassis, but the heat will rise and flow out of the lid vents. This heat is much less than that on the immediate power output heatsinks.
Assuming the amplifier had adequate venting, the components inside the case, except the output transistors themselves, only warm up a bit;
One thing I think is really cool about Pass Labs X and XA amps is they further reduce thermal stress on caps because the output boards are completely devoid of any capacitors; They mount the power supply filtering caps on a centrally located PCB lowest in the chassis in the coolest spot possible. These caps will hardly have but a few degrees of "deltaT", that is change above ambient temp; The heatsinks can get nice and toasty but the MOSFETS are designed to have a T_max many times hotter than the amp ever sees in practice. Luxman stuff is also super reliable and designed extraordinarily well; The Luxman engineers are laser focused on design implementation and think 20-30 years type of service life.
I bought my first "real" stereo amp in 2005: Then, a few year old McCormack DNA 0.5 SN 123; This design has the caps in the worst thermally conductive path; directly adjacent to the output transistors. The heat WILL conduct nicely on the heavy copper PCB traces directly to the caps; and the caps are also close to the heatsinks.
These caps are kind of run of the mill 4,700uF 63V 2500 hour service life, rated for 85 deg C; Guess what?
My brother has that in his system and when I visit him I see it is still sounding wonderful; There is NO sign of venting or any hum/ripple coming through; I have had that amp's lid off numerous times through the years to show him and, well I just really like amps ;)
Moral of the story:
A 9 year old well made solid state amplifier that was treated kindly (was not stuff in a closed off cabinet, used on a a carpet, had plenty of inches above and around the unit, was not used outside in Yuma Arizona in direct view of the sun...etc), will still have years and years of high quality service life; Rest easy;
