FWIW ... I've owned a Marantz SR5007 for the past 20 months, paired up with three 4ohm speakers (MartinLogan Motion 40s and a Motion 30 center) and a pair of 5 ohm surrounds (ML LX16s).
During the winter months, things seem fine (thermostat set around 64 degrees).
During the summer, however, the AVR can get pretty hot to the touch (we don't run the AC until temps reach the upper 80s) ... to manage the AVR's internal temp, I've run a small Cool Components dual fan at about 1/2 to 2/3 speed (full speed is too loud), and this helps keep the AVR from becoming too hot. If I'm in the adjacent dining/computer room (on a really warm day) I'll even point a floor fan towards the unit and this will keep things very well in check.
Additionally, I've designed a shelf that I can pull the AVR out about 4" from the armoire in which it is placed ... and finally, there is almost 3'' of space above the SR5007 ... all for as much breathing room as I can manage.
Nevertheless, I've become tired of trying to manage this situation - and worry that, because of the "hot to the touch" temp that result sometimes without the (noisy) fans involved, that I may be overworking the SR5007, resulting in a shorter life span for the unit.
Therefore, I decided to add an amplifier. I was all set to order an Emotiva UPA 500 (120watts per channel @ 4ohms) for $349 and provide my hard working Marantz AVR some (IMO) much needed and capable assistance.
I was really hoping that Emotiva had an offering somewhere between the (120wpc @ 4ohms) UPA 500 and the (330wpc @ 4ohm) XPA-3 / (300wpc @ 4ohm) XPA-5 ... something in the 200wpc range ... but they don't.
When I asked about b-stock inventory at Emotiva, I was told that the UPAs are already marked down as far as they can go, and that the XPA-3 was selling for $650 and the XPA-5 was at $800.
I ordered the XPA-3 and will use the Marantz to drive the surrounds.
I haven't received my RCA cables yet ... I'm looking forward to hearing how an amp will "open up" the sound coming from the ML Motion speakers ... and I expect that the AVR will be able to drive the surrounds without much difficulting, and therefore retire my Cool Components unit.