You have been unfortunate with two faulty subwoofers from KEF. The issues with reliability from KEF subs generally relates to the PSW2010 model that was supplied with the original KHT2005. That unit was sold in the thousands and a great number suffered a fault. To be fair to KEF they owned up to the issue early on and replaced the amp board free of charge on units all through the warranty as you would expect but also well beyond into year five and further.
It was indeed the 2010 model and I am well aware of the issues with that particular model. Kef denied any issue for a long time till internet forum pressue and many many unhappy customers finally got them to change their stance, well, that and the fact they got caught using employees to post on the forum as happy customers, but thats in the past now anway. I wont mention the 50p fix they charged £80 a time to repair.
The newer subs do indeed seem better, but some new ones have shown the odd sign of dying like the 2010's did.
BK have of course had the odd issue, but their feedback is generally very good, and their fixes to problems typically very quick and satifactory. Suffice to say, I can link to many more customers banging on about how good their BK's are than I could about the lower end of the Kef range that sists in the same price lime up as BK's subs. BK biggest criticism is that they generally dont communicate that well via e-mail. Once you order you generally get no further communication till your order is ready to dispatch, sometimes even if you mail asking for an update, and for some this has been unacceptable, which is fair enough I guess. A quick phone call has almost unanimously solved that problem though. To be fair to Kef, I cant recall ever seeing any comment on issue with the finishes on their products.
Finally, the independant testing of BK's subs has confirmed they shoot well above their weight when it comes to purchase price, and a £450 Monolith will put any equally priced Kef sub to shame.
I'm not here to pick on Kef, but at this price range the BK's are very hard to beat in performance terms, and even with longer than many delivery times (because each sub is built to order), the vast mojority of customers are happy they waited. Of course, I wouldnt wish to be to blame for any loss of sale of Kef subs you might suffer due to my comments, but sometimes things need putting into perspetive.