That's correct. The NT 6 improves on the ER4S with much better subbass response and more natural, fleshed-out bass overall. Someone asked a similar question here: http://www.head-fi.org/t/478568/multi-iem-review-295-iems-compared-vsonic-vc1000-added-09-03-13-p-760/11265#post_9729619
Thanks Joker. I'll keep the NT6 on the back burner for now due to the cost. I'm going to check with Project86 regarding the Cosmic BA4R. I'm sure the NT6 is technical superior, but the latter is much more wallet friendly.