Vaggelis,
1. Automatically enable Read-It-Clearly in Full Screen Mode - As PDVD says, may cause problems with older GPU's. I do not have it turned on and I can see/read everything on DVD's clearly. So, I can't say if it's something you should enable or not. I'd leave it alone unless something doesn't look right on a normal DVD.
2. Play DVD/VCD more smoothly between 4x/8x speed - I would enable this if you experience playback issues such as Frame skips/stuttering. Otherwise, probably not needed.
3. Audio Output settings - I would need more info on your current audio setup to give you an answer.

Regards,
James Cossin "Only the dead have seen the end of war"
PC Specs:Q6600 @3Ghz,4GB Ram@1066Mhz,750i SLi FTW @ 1333Mhz FSB,(2) EVGA GTX 470SC 1280MB,X-Fi Platinum,Nvidia Edition Antec 900.
Acer H5360 3D Projector, 92" EliteScreens Screen

Thank you for your answer...

1. I have icore7, so you think that I should leave it off and turn it on only if I have issues with the playback?

2. The same as the 1.

3. I have 5.1 and sound card the x-fi elite pro of Creative.

Vaggelis,
I have a very similar audio setup as you, the way I have mine run is from the X-Fi to my 5.1 surround sound by a 3.5mm jack to RCA ( SEE HERE ). In X-Fi, I have CMSS-3D enabled (surround virtualization). On my 5.1 surround system I have my settings set to Multiple, that way it plays audio over all channels of the 5.1 and it lets the X-Fi do all the work.

Also, yes I think you should just leave the options unchecked.

P.S. Sounds like you have a gaming rig. Care to post more on your system specs? Always interested in other peoples builds.

Hope that helps,
James Cossin "Only the dead have seen the end of war"
PC Specs:Q6600 @3Ghz,4GB Ram@1066Mhz,750i SLi FTW @ 1333Mhz FSB,(2) EVGA GTX 470SC 1280MB,X-Fi Platinum,Nvidia Edition Antec 900.
Acer H5360 3D Projector, 92" EliteScreens Screen

I have logitech Z-5500 and I connect them with x-fi elite pro with 3 jacks with 3 colours, black-orange-green. At the output mode at PDVD it gives me the following options:

Stereo
Dolby Surround Compatible Downmix
Dolby Virtual Speaker
TruTheater Surround

So what do you think I should put?

I have icore7@3.06, 6 GB memory, GTX 470 EVGA nothing too much..

Thank you in advance!

PS. You say: On my 5.1 surround system I have my settings set to Multiple, that way it plays audio over all channels of the 5.1 and it lets the X-Fi do all the work.

I can't understand where is this?

Vaggelis,
Sounds like you wouldn't need the same settings as I do, you probably need to have your setting in PDVD set to: Dolby Surround Compatible Downmix.

My best judgement is that it will let your Z-5500 decode the audio and spread it across the 5.1

Regards,
James Cossin "Only the dead have seen the end of war"
PC Specs:Q6600 @3Ghz,4GB Ram@1066Mhz,750i SLi FTW @ 1333Mhz FSB,(2) EVGA GTX 470SC 1280MB,X-Fi Platinum,Nvidia Edition Antec 900.
Acer H5360 3D Projector, 92" EliteScreens Screen

Thank you friend!

Your welcome, glad I could help.

Br,
James Cossin "Only the dead have seen the end of war"
PC Specs:Q6600 @3Ghz,4GB Ram@1066Mhz,750i SLi FTW @ 1333Mhz FSB,(2) EVGA GTX 470SC 1280MB,X-Fi Platinum,Nvidia Edition Antec 900.
Acer H5360 3D Projector, 92" EliteScreens Screen