I have two MCL-2A with Beovox MCX35, one MCL-2A with S80 and one MCL-2AV with BL4500 connected to a MCL/ML.
My impression is that MCL/ML can handle at least 4 sets of speakers without troubles. The volumen goes up quite high, and the sound is still quality. The amp. in the BC8500 is basically the same as the MCL/ML, but a little bigger, so you should not have any problems.
Prior to the MCL/ML and BS9000 I had a BM3300, which was used to drive the MCL (same speaker config) and a pair of M75. Here I found that when I turned the volumen up a protection circuit cutted in and lowered the volumen. If I when turned some of the link rooms off, the problem disappeared.
My conclusion is, that it is not possible to damage the equipment, and if you want more power you will have to turn off a link room or two.
There is no difference between connecting two sets of speakers to one MCL-2A and connecting them to two different MCL-2As. The BC8500 will experience the same load.
Living room: BV7-40 mkIV + V8000, BL5, BL3, BM1 and BS9000. Bedroom: MX3000 and BL4500 on MCL2-AV. Around: PentaIII, CX100 and MCX35 on ML/MCL + MCL2-A, BeoPort and BL4 on ML, BS3300 + M75 as stand alone, BC6000 + BC600 and BT1100, LC1, LC2, Beo4, Beo5 and BL1000, BS2 and A8, EarSet2, Apron, Coffee mugs, Enamel Bagdes, Bath towel, Keyring, Books, Lots of miniature and the Bottle opener. Office: BC2300 + BL2500 and BS3. Summer house: BS Century.
Addicted? Oh no.... ;)