First off I love my polk sr5250, they sound f`in amazing. I had them over a month or so now, and there is no way I will trade these away. But however, I noticed that I need lower lows than what the sr5250 provides. Its a shame that polk didn't make a 8in sr series, and I'm left with the mobile monitors 8in (only size that will fit under the rear seat). So I was wondering what are your thoughts on mm840 sub and if there are any other 8in subs I should consider, let me know (max 4in depth). I chose this sub because its a polk (sr series really made me a fan), and it fits my back seat perfectly.