I own a pair of 201s and have compared the 501s at home. Both sound similar -- tonally well balance with good freq extension, quick and very musical. Although small in size these amps are built solid and look very attractive. They are designed to be left on 24/7 (little current draw) and run very effeciently. I haven't heard the older model JR amps.
Wadia 861>>JR 201s>>B&W804 Spk.
Wadia 861>>JR 201s>>B&W804 Spk.