I think my NAD320BEE goes great with my 601 S3's. Perhaps a more powerful version of this amp?
I think the amp is not as warm as a Marrantz (but I've not listened to one), certainly isn't cold though, very exciting well controlled sound. (They are certainly not as warm as my Audio Technica ESW9).
Perhaps wait for the opinion of someone who has tried both.
For the type of music you listen to I would say go for a NAD amp with your B&Ws but everyone is different, it may not sit right with you.
What does the 'warm and soft' mean in relation to the Arcam?
Or looking into a C370...the plot thickens
What does the 'warm and soft' mean in relation to the Arcam?