Here is another vote for the ESP design. I'm currently building a 6-channel amp based on it (4 channels complete!), although I'm counting on my powered sub to pick up the LFE. 60W (100W with higher rail voltages) is quite sufficient for many people's needs, although you may wish to use an alternate design for the sub.
These amps can also be constructed with very cheap output transistors. (US$0.07-$0.60 for MJE2955) This is very comforting when you destroy them, and you can always use something like 2SC1302 (US$4) when you are more confident of your construction.
My suggestion is to buy 3 of Elliot's boards and build your 6 channels from them. They will make you happy, and you won't need to spend the same amount of time on heatsink fabrication that a monster amp would require. Very little of my amp construction time has been spent on wiring: it is mostly the mechanics that eat up time. (and you can always bug your cousin to build a more powerful sub amp in the future.)
ESP amp cost for 6 channels, USD. I warn you that I /invariably/ underestimate costs, so take this with a huge grain of salt. If you have access to lots of usable surplus parts, it may actually be cheaper, although I'm assuming you don't pay manufacturer prices for most items, and strike a balance between dirt-cheap construction and premium passives.
Output transistors: $6-$50
Other transistors: $30
Passive components: $50+
PSU
rectifiers: $18
capacitors: $36 for 35v rails, more for 42v
xforms: $120
Case: $30-$100
Sinks: $30-$100
I/O connectors: ??
Wiring, solder, tools, etc: ??
