FURMAN, PS AUDIO, ISOTEK??

None of the above. Start with noise-filtering power cords by LessLoss (DFPC Original or Signature; $595 and $1149 ea., respectively). There's no risk of inhibiting dynamic performance with these power filtering power devices, and their multitudinous benefits are immediately obvious. Once hooked on those, you might consider the LessLoss Firewall power conditioner. That's some serious performance enhancement. I own all three of these products (3 Signatures, 2 Originals, and 1 Firewall) -- so I'm speaking from my own experience here.

The Furman is a good unit as long as it is not overloaded. It is used a lot where AC voltage is variable, as it will try to keep the line voltage stable (it has a circuit for switching taps on its isolation transformer).

It is most often used in studios. As I mentioned before though, you do not want to push it hard. I would not use it with a power amplifier unless its a small transistor unit.

I'd go with Isotek - I'm biased since I own a Mini-Sub II. PS Audio units are are energy wasters with mediocre performance. Stay far far away from Equi-Tech products,they sound closed-in, and have a horrible build quality. My equi-tech had "reset" issues, and when I took the top cover off, I was amazed at the sloppy workmanship there was - and at the amount of aluminum shavings that where inside the unit. Buy an Iso-Tek or Transparent Audio unit, and don't look back, just enjoy your music knowing you've got a REALLY quiet background, and are using "protection." All the best. - Sorry that I haven't heard Furmans.

With any power conditioner that has magnetics in it (the Furman and the PS Audio both do) should not be run past 50% of their capacity, else they will degrade things rather than help. The reason is distortion of the AC power, which usually becomes pronounced once a transformer is past 50% of its capacity. This make diodes more noisy, power transformers more noisy, and likely is the reason you see variable opinions about the usefulness of power conditioning.

For the most part, we recommend that people avoid using AC conditioners with our amps. IMO, the best use of conditioners is with the front end of the system.

Now there is one power conditioner that really works and can handle a lot of power. It was made by Elgar and is not a high end audio product. But right up to full capacity it can make a perfect sine wave at its output and is the only conditioner I know of that can do that. It is mechanically noisy, so to use it, it is installed where your breaker box is and then the line that runs the audio room is connected to it. They are not cheap, and Elgar does not make them any more :(

Thanks a lot to everybody, it has been a great help.
The conclusion is going step by step so I will start with a couple of power cords.
Any recommendation on this??

You didn't mention power cords. What do you have? I would address this first.
And how much are you prepared to pay for how much improvement? Generally speaking, to get some control over the incoming current is quite expensive. But still you could improve the situation for a few hundred dollars if you wait and buy used.

The very wide and disparite opinions expressed about power conditioners of all sorts makes me wonder if you can say that they will upgrade your system in any general way. There are exceptions to this if there is a particular problem. For instance power regenerators for people who have power brown outs and peaks who wish to stabalize their power. Other specific examples are out there I am too lazy to list the ones I can think of. So unless you have a very specific issue invest you upgrade money eleswhere.

you have nice gear...if you can borrow some pieces and hear how it sounds you'll be way ahead of the game. If you do not have a dedicated circuit for your stereo then I would do that first and add a power cord to the DAC....if you have fairly clean electricity you might not need a conditioner. I use an Exact Power EP15A which holds the current at a steady 120 volts and protects against surges and brownouts.