Well it's been a month Iv'e been playing Boomers on my BTB and XL's on my SR. The difference I see, feel, and hear is... Xl's have less bottom, sweeter mids, and brighter treble. Boomers have thicker bass tone, aggressive mids, more punch, and crisper but mellower treble. Boomers are also smoother feeling, XL's are coarser. Just my own little comparison. Who else agrees with this conclusion?