When an amp puts out 90 watts....

Fin,
I think that is indicative of sn amp with higher output impedance, usually but not always an attribute of tube amps. An amp like that will probably perform best into higher impedance speakers, ie 16ohms, which is not common. Its a special breed that needs a special mate. My recollection is that pbn is probablyof the more typical ilk, impedance of 8 ohms or less. Probably not the ideal pairing, but workable.

I have seen some pnm impedance measures in stereophile that show wide impedance flucuations from 4 to 16 ohms at various frequencies. Far frm the constant high impedance that an amp like that would probably do best with.