The rejuvenation of FPB 600 after recap

Just have experienced a new thing, a friend of mine bought an used FPB 600 but the sound was not so dynamic and even weak in bass, how could that be for KRELL power amp?

After reading some post in Agon, I helped him to replace total >240 pcs. of electrolytic capacitors in total. The difference is tremendeously huge. 

The dynamic is first rank and bass is full and amazingly strong. 

It is now affecting me in good way because I want to buy a big KRELL too. Knowing this FPB60P is already more than 2 decades. Is it rational that I go for this FPB600 (atttactive price as low as 5000 USD for a decent looking one, but for sure those cap need replacement after this experience)

I will be driving a pair of JBL array 1400 and a pair of Watt Puppy 5.1. What would be your suggestion ?

If you like what 240 new caps did, try replacing the handful (probably 4) of 20 year old diodes with newer faster higher quality. I lean more McCormack myself, but better diodes improves everything.
I think you are talking about rectifier for power supply. The FPB600, however use rectifier bridge 
If you have a choice, higher temp caps last longer.

But yeah, that amp may sound better than it did originally. Electrolytic caps are so much better, lower inductance than they used to be.
Panasonic makes great ranges of low inductance, low ESR caps. FM among them. I'm sure others do too, it's been a long time since I recapped an amp, an old Yamaha P2050. :)
Then purchase a high quality bridge rectifier (IXYS - FRED) from Parts Connextion.