The W series, including the W40 (4BAs) are made for music listening consumers so the sound signature is more general population. The targeted freq. are the ones that studio recordings usually boost to please listeners. The UM series are the original expertise of westone, they are made as true monitors for musicians, this means better live reproduction, better low frequencies to reduce crowd noise, and most importantly less fatigue by rolling out extended high freq. This makes the sound signature different than hi fi sounds general population likes, and the W series was issued to address the complains of general listeners who bought the UM series and critisized them as if the are aimed to general hi fi. Summary is W series is more enjoyable by most music lovers, clearer high freq, yet more fatiguing than UMs. UMs have in my opinion a bolder sound signature for people who like to be surprised by their music listening, listen for longer periods, and prefer certain guitar driven music. I enjoy the UM series for rock blues jazz stuff more than Ws
Thanks a lot looks I'll be looking at the UM series. Thanks a lot if the UM50 comes out soon this quarter I'll wait it out then.