the 901s had an ability to do something that other speakers at that time could not do (tho they lagged in other criteria compared to some)
if they have been refurbished recently then try out some Maggies - used 3.7i's can be had for $4k - new is %6k to $6,400 for various wood strip and cloth options
if not, you could do that as a low-cost 'upgrade'
if your amps will drive a $10k speaker well, then you can achieve stunning SQ
Ki3
bigger maggies
various others...
but I'd reserve some $$ for room treatments and maybe a few hundred for an isolation transformer, and some galvanic isolation devices
if they have been refurbished recently then try out some Maggies - used 3.7i's can be had for $4k - new is %6k to $6,400 for various wood strip and cloth options
if not, you could do that as a low-cost 'upgrade'
if your amps will drive a $10k speaker well, then you can achieve stunning SQ
Ki3
bigger maggies
various others...
but I'd reserve some $$ for room treatments and maybe a few hundred for an isolation transformer, and some galvanic isolation devices