Classic preamp for Plinius SA-102: need advise

I would definitely look for a used BAT VK-5i over any of the SF line. I love SF amps, but their pre-amps sound kind of lifeless and dull to me.

Meanwhile, I have received this message from Plinius:

"Please have the preamp checked to see that is has no DC at its output before you use it as the SA102 is direct coupled."

Can you explain me (slowly...) what this means?

It means that there is no output transformer or capacitor that separates DC-component out of the signal.
There are two devices that separate DC off the signal: transformer and capacitor.

Preamps can also be as SA102 direct-coupled.

The risk of having DC is high in all direct-coupled output stages whether it's preamp or amp and in case with Plinius you can only pray for its unsinkable performance that will only depend on quality of preamp. So far I heard of no failures whatsoever happend with Plinius gear in general but some of preamps do have a DC-component in its normal operation that you should be aware of and check DC-voltage with voltmeter if any at the output with preamp on and volume control at minimum or mute.

The largest danger of DC when it's present at the speaker since the voice coil will work as water-boiler and increase its temperature and than burn even taking away diffusor.

I had the CDLAD and tried the Classe CP 47.5.
If you compare these two you'll notice the CP 47.5 will show you how much potential the SA-102 really has.
You will also gain a better calm and control to the overall performance. Further the CP 47.5 has a good compatability with the SA-102 (impedance match well!)

The CDLAD's bass seems further away, it also has less body in the upperbass/ midrange. The soundstage and dynamical impact will also be bettered with the CP 47.5.
With CDLAD, vocals and guitars will seem much closer and drums and basslines will sound lesser/ thinner without there appropiate weight and richness.

I had 3 friends in and and performed a blind test, no-one prefered the CDLAD before the CP 47.5.
I can also tell you that there is an uppgrade kit avaible for the CP 47.5. With this uppgrade done you will notice a better blackness/ a better background silence, and some improvement of (especially inner) resolution
and microdynamics.
I had the CDLAD mark 1 and it had such an excessive gain through the XLR connection, the noise levels severely disturbed the pleasure of listening. I had mine sent back to Plinius for this.

I've heard the Plinius SA-102 with the AR LS-5, and it was definitely a winner combo. If you talk to avid AR fans, many think the LS-5 is one of the best reasonably priced preamps ever made by AR. I would agree based on my limited experience with their models. Good luck finding a used one though because I rarely see people parting with them.