B&W 801 separate amplifier just for bass drivers

You can use two different amps -- as long as their input sensitivity is the same. I can't recommend specific products as I don't know the cut-off frequency of the mid-highs.
Of course, we assume your preamp has no trouble driving two parallel loads?

Thank you Adp1

You're right. I strongly evaluate other brands. But I still have a prejudice concerning Krell caused by older designs that sounded harsh/bright/brute.

Have they musically improved a lot in the last 10-15 years?

AK

AK, I've heard FPB series amps some time ago and didn't find them harsh. It depends on other equipment as well. McIntosh and Classe amps sound quiet nice with B&Ws as well.

Thanks Audp1

Which of the Amps you name should I try first? What are your favourite products?

Andy

I heard N801 with Classe and Mac equipment. I thought they sounded very smooth with Mac but had a little more life in them with the Classe. If your taste in music is mainly classical and jazz, I wouldn't hesitate to recommend McIntosh. I beleive the amps I heard were MC501 monoblocks. Unfortunately I can't recall the Classe model but it was one of their bigger amps.