Currently, I am using a set of amplifier "circuit boards" I picked up at an electronics flea market. They were what I was using on my old pro-logic surround system. They run about 7 watts RMS output each.
These will be replaced with more substantial amplifiers as I proceed. You would be amazed at how loud it can get even at that power level.
Personally, I would not worry about the receiver output rating at 4 ohms vs 6 ohms vs 8 ohms because speakers are anything but a constant impedance.
There are two possible problems with an amplifier driving low impedance speakers:
1. If you plug 4 ohm speakers into an amplifier rated for 8 ohm loads, it is possible that its power-supply will not be able to supply enough current on very loud passages when listening at high volume levels. This will make the sound distort or sound muddy. If it is a multi-channel amplifier, it may run into this problem if all channels are driven to max output at the same time even when connected to speakers at the suggested impedance. (unlikely with music) This class of problem is more likely to occur on inexpensive receivers that have marginally designed power supplies with small (lightweight) transformers and small filter capacitors. In fact, some are guaranteed for their rated power level with only two channels driven simultaneously.
2. If you plug 4 ohm speakers into an amplifier rated for 8 ohm loads, it is possible that it will overheat if driven for long periods of time at maximum volume if its heat-sinks are too small. (This actually is more likely to occur when the amplifier power supply is able to supply sufficient current on loud passages.) This overheating could cause damage to the output transistors if they did not have circuitry to protect them from high temperatures.
If you keep away from the most inexpensive amplifiers, the odds are you can use any of the DIY speakers with just about any amplifier rated over 5 watts a channel and enjoy fairly loud sound in your theater no matter what load impedance your speakers present.
Now...to keep things interesting... I have a pair of monaural amplifiers I built in the early 70s that were (conservatively) rated at 250 watts into 8 ohms. I personally measured somewhere near 600 watts into a 4 ohm dummy load driven with a 1000 Hz sine wave for durations of a few minutes. (without them clipping or distorting) They weigh about 30 pounds each, most of the weight being the power transformer and heat-sinks. They play for about 30 seconds after the power is turned off. (They have very large filter caps in their power supplies)
I used to use these to drive a pair of Ohm Acoustics Model "F" speakers. They were rated at about 3 ohms. On a very hot summer day in a un-airconditioned second floor apartment, one of them did power itself off when the heat-sink temperature rose to where the thermal cut-off opened. This was after driving them at high volume (then the landlord downstairs was out for the afternoon) It did cause me a bit of concern, but once I realized what had happened, I simply turned the volume down a bit. They did not suffer from either of the flaws I described above.
I'll eventually use these to drive a DIY subwoofer (a future project) and a buttkicker.
Lastly, according to the Audax web-page that describes the DIY speakers I am building:
The left and right channel speakers are 2-way vented systems with a 4th order acoustic in-phase crossover at 2650Hz. Sensitivity is rated at 88dB/2.83v/1m. Response is within +1.6dB from 100Hz to 20kHz. The low frequency -3dB point is 50Hz. System impedance is 8 ohms.
The center channel impedance is above 7.5 ohms throughout most of the low-frequency range. The minimum impedance of 5 ohms occurs at 4.5kHz. This is frequency is high enough to be of little concern. Phase angle lies within +40o over the entire frequency range. This is an easy load for typical multi-channel home theater receivers.
Looks to me like the Audax HT design is not a 4 ohm design after all.
Sorry for the delay in my responses these past few days. I was one of those in North Carolina without any electric power for the past 5 days. (Mother Nature, an Ice Storm, and Duke Power staff reductions all had a lot to do with this)