Hi,
I have had alot of gear with Elna caps in them. Marantz uses alot of those caps. There are different series, (Silmic, etc..) in there lines. The thing I would be most concern of is since that receiver is pretty old and those are stock caps, they might be leaking, or not tolerant to their values. (I measured some Elna caps out of my old Forte F44 pre-amp and they were about 30-40% off of tolerance. But this is dependant on heat, humidity and usuage. I beleive caps have a shelf life, like batteries. I would personally change mine out on a typical peice of gear after about 5-7 years (I have a Vimak DS-1800 DAC here with 90% of the caps leaked and values of the caps are way off). This will lead to failure or quirky operations in some instances.
I would believe the Elna Silmic is the best version they produced and some favor the sound of these caps in certain applications over some of the more favored brands.