It's really hard to get anything decent on a $400 budget but I like your first three links over any of the other suggestions so far.
As for ohms, there is no impedance "matching" between receiver and speaker. Impedance matching only applies to transformers, not solid state audio amplifiers. The impedance rating you see on a receiver is actually a current capacity rating expressed in terms of minimum load impedance. If it can't handle lower than 6 ohms for example, don't put a 4 ohm speaker on it and don't double up 8 ohm speakers on it.
