Ola Fernando:
I use the Yamaha AX592 integrated amplifier. It fits the nature of the work I do as it connects two tape decks, a CD player, phono, if needed and I still use the old records for special effects, am/fm if ever needed, and I can mix down to either or both tape decks or from one to the other--it's and amazing little amp. It also supports two sets of speakers: monitors and commercial speakers for listening.
The amp also has a "straight" through feature which cuts-off any coloration from the amp itself if needed.
I put my Yorks up for sale as soon as I plugged in and listened to the KRKs. Mr. Q twice is correctomundo about the Tannoys; they do cost more new methinks. I don't but used gear very often.
Because the KRKs have a larger woofer than the Yorks, as I mentioned 8 inches opposed to 6.5 inches, they give a bigger and rounder sound. The low end on the KRKs is better, as well as the high end. Of course if you go to more money, there are monitors that will blow away the KRKs. For the time being, I can get along with the KRKs.
But, I'm always reading here and listening there and can decide to upgrade anytime.
Ciao,
Green Hornet