Well, yeah. First of all, you can put nearly everything to control on sliders, it´s just a question of programming. Means you can´t do this globally, you have to do this for every singe sound or combi you want to use. Still want it?
Check the manual on how to connect functions to the sliders. Hint: There is a page (in the PC3 editing) where you can find all the controllers, also all sliders. You need to have an EQ in your FX chain, connect the gains of the desired frequencies to the sliders. Voila.

to answer your original question - no, it is not possible. not with the master FX.
the new Artis/Forte do have such quick access 3 band EQ on the front panel...

Thanks KaffiMusic and M.Dudas for the help. It will be ideal to have the master eq control easile assigned on the sliders, but (correct me if im wrong) as i understood, i can put a equalizer on the fx chain on a setup for example and assign the sliders to control its parameters, and kindda make this setup a template to create any other that i need this function.

At this time, im connecting my pc3k on 2 mono channels of a behringer mixer 1202fx (not the best i know) to have this eq controls, but im afraid to degrade the signal over the mix, im my other topic im actualle asking for tips in this matter. i will try your suggestions and post here back, thanks again

Yes, you could do some kind of template and put an EQ on a AUX-channel. But be aware, this might influence the FX on some of the sounds you use, depending on how they are programmed. There might be some that already use a AUX channel, and that one is overwritten inside the setup. But since most sounds use their own inserts, that should mostly be no problem.
But consider this: To my experience, the PC3 has some very well balanced (exept the volume) sounds, that really fit nicely into a mix - also in live situations. If it does not sound right generally, than it´s usually a job done with the mixing - and now its globally done for all the sounds, to adapt it to the momentary acoustic situation.
I know people tend to rise presence and high freqnencies, that might make them "cut" through to a bandsound. But thats not good, because all try to do that. The result is bullshit and a mashed up sound.
The danger of messing up everything with a personal EQ is bigger than just leave it like it is. Unless you REALLY know what you are doing.
If it´s a special effect for several sounds, you can program it into them.

hmm, i undeerstood, again thanks, nothing like talking with experts I will explore this option when possible and try balanced cables with DI in order to see if i get some improvement on the sound definition.