smm111) Etymotic uses mmcx connectors, so theoretically yes. However, these cables have pre-formed hooks that are meant to be used with IEMs with cables that hang over-ear. I can't see the hooks working well with Etymotic's design. You might not be able to wear them at all with these cables on. (the hooks might curve back towards your cheeks and push the ER3XR out of your ear)
2) Don't buy cables looking for improvement in sound quality. There might be some very slight differences, but it's never worth it. I'll only consider buying cables when a) the old one broke or b) you want a prettier looking one.