CAV 6.6 with multiple speakers per zone

Has anyone installed a CAV 6.6 with more than 1 pair of speakers per zone? The installation I inherited has several zones with 2 pairs of 8 ohm speakers wired in parallel for the zone. The CAV 6.6 manual says that you need to install speakers with a resistance of 8 ohms into the zone, which will put out 20 watts per zone.
I have one zone with 3 pairs of speakers, and for that zone I installed a used Russound D250LS triggered with an impedance matching volume control, and that works very well. The thing is, I would rather not buy 4 more of those, with an equal number of volume controls.
I realize I could simply install the impedance matching and settle for lower sound volume, and maybe I will do that, but 2 x 8 ohm speakers in parallel is only impedance of 4 ohms, how bad is that really for the amp? Or is it simply Russound's interest in selling more hardware? Anyone run into this before?
After listening to the amplified zone in comparison to the non-amplified zones, it seems clear to me that the amplified zone sounds noticeably better. Whether the amplifier in the CAV is damaged by the lower impedance is still unclear, but it would seem unlikely considering the previous owner had it connected this way for about 10 years.
Of course, there are many ways you could install amplifiers on each zone, including several 2 channel amps on Amazon which are in the $20 - $30 and which would power a 4 ohm speaker. This leaves the amplifier constantly on, unless I find or create some way to switch it on and off via the CAV, or get an amplifier with music sensing, which would increase the cost of the amp. Since we are talking about actually for me 5 zones = 5 amplifiers, you can see the cost stacking up pretty quickly.
Another alternative would be to purchase a 12 channel Russound amplifier and use triggering from the CAV to turn each zone on and off. A new D1650 runs $999 at Crutchfield, but I found a used R1250MC on eBay for just over $200, which provides power triggering for each zone, and 50 watts into 4 ohms or 35 watts into 8 ohms per channel. Since it works with 4 ohms, I won't even need to install impedance matching on the zones containing two pairs of speakers.
Of course this should have been done during the initial installation, but it appears there are ways to improve a poor Russound installation without breaking the bank.