So what's the best Linux distro for Pianoteq 5?

Tango Studio is for me the more stable and easy distribution. It works perfectly. KX Studio is beautiful but a little less easy IMO. Most of the distros share the same applications, but the graphical environment differs.
I agree with Ross about the VSTs, and all the third party software...

But, if what you want is a dedicated pc just to play Pianoteq and record it, Linux works like a Swiss watch. And Ardour (included in the distribution) is a top of the line DAW for recording.

If you want to do more complex projects with other instruments... then go with windows or Mac.

Don't forget that the Linux world is a little special, you will need a little time to learn somethings. But if you just want to play, you can be ready 10 minutes after the installation of the distribution.

For the smallest I don't know, but for real time kernel, go for Tango Studio, since KX Studio and Ubuntu Studio don't have a real time kernel but a Low latency one.

Now, if you just want to use Pianoteq and don't need all the other extras, you should find a way to begin with a very light distro, Lubuntu for example, and then install a real time kernel and jack on it.
But that is out of my competence.

You have to download the good 2.2 iso file here (i386 or amd64, it depends on your system), probabaly the 64bits version with a recent pc:

http://tangostudio.tuxfamily.org/fr/pla...dio-update

You burn the iso file on a cd, and you run your pc with the cd inside. The pc must start on the cd.

You can try the distro before install if you choose the option "Live (realtime)" or something like this...
This way the distro is not installed but runs from the cd.
If all is ok and works fine, you are ok.
If you decide to install, choose "Graphical install", and the process will be easy.
You will be asked to choose the computer's name, the user's name, the passwords...

Keep us informed if you have problems

On UBUNTU STUDIO all works fine without doing anything else.

But it's just THE ONLY ONE Linux distrubution that works EXACTLY LIKE WINDOWS.

Now I need someone that explains me how to "install" the -rt kernel on UBUNTU STUDIO ...

So ...

Installing Linux-Realtime in Ubuntu

Linux-Realtime can be installed on both 12.04 and older versions of the Ubuntu distribution.

For Ubuntu 12.04 (Precise Pangolin) you can directly add the PPA from the following command.

        $ sudo add-apt-repository ppa:abogani/realtime

For Ubuntu 11.10 or older you need to edit the sources.list file to add the repositories manually.

        $ sudo gedit /etc/apt/sources.list

Then append the following lines at the end of the file

    deb http://ppa.launchpad.net/abogani/realtime/ubuntu precise main
    deb-src http://ppa.launchpad.net/abogani/realtime/ubuntu precise main

Save the file and update the apt repositories

        $ sudo apt-get update

You are now ready to install the Linux-Realtime on your Ubuntu system

        $ sudo apt-get install linux-realtime

(Last two steps are also valid for PPA method in Ubuntu 12.04)

This will update the Linux kernel to the version 3.2 with realtime version. With the Previous version of your linux kernel intact which you can choose from the grub boot menu at the boot time.

Note: Booting into Real-time Linux is not recommended for day to day work on Ubuntu as the performance with Real-time Linux is slightly slow and sluggish with normal desktop environments (such as gnome, unity etc) and apps than with the normal kernel OS.

I mean about operativity.
Ubuntu Studio performance has no comparison with any MS Windows Os.
On the same computer (the first Atom on the market ) with Win 7 Pianoteq 5 just doesn't run but with Ubuntu Studio 15.04 it runs fantastic ( poliphony apart )