From my experience, I'd tend to point the finger at your Ittok. I went from an Ittok to an Ekos mk2 and that stretched the frequencies out at both ends. Before that I wasn't really getting the bass on Massive Attack's Mezzanine. I knew there was something there but it was muddy, indistinct.
If you do go for a used Ekos, the thing to check is the bearings of course. These can easily get lunched - I've done it! With no tracking force on, so that the arm floats freely, you should be able to move the arm around in both dimensions with no notchiness or friction at all. If you place a 1cm square piece of paper on top of the arm when it's floating freely, the arm should fall to it's lower limit of travel.
The nice thing about arms is that you can buy internationally, just so long as they've got the right packaging. Also get them to get a Linn dealer to remove the arm, or get the dealer to inspect it and package it. The counterweight should be removed. Mine was sent for repair through the British post to and from Glasgow, and if it can survive that it can survive pretty much anything.
Also you don't mention a power supply for the LP12. I know this shouldn't make such a difference, but believe me it does - I use an Armageddon and before that the LP12 didn't time that well, afterwards you can hear the syncopation of a track, why drummers do those funny little drum breaks - they're getting back on the beat or changing the beat.
I'd try those 2 things before anything else. However, Naim don't really do trouser flapping bass, or at least not at the price range I operate on. They tend to prioritise speed and control before anything else. I run SBLs actively and on Massive Attack's Angel you get the 'bump, ting, b-bump, ting' where bump is a bass drum and ting is a cymbal, but deep and fast as it is, it never hits me in the chest, the drivers just aren't big enough to shift enough air to do that.
That might just be SBLs though - I've never heard Isobariks but they were famed for their bass back in the day, but also for being a pig to drive. But 2 x 135s should do something.
Before the SBLs I had a pair of Linn Keilidhs which had 2 8-inch drivers. The only thing I miss them for is playing Chemical Brothers 'Out Of Control'. The bass might have been all over the place but it was exciting. That was with a single 250 though.
I do apologise for Linn / Naim's pricing policy in the US. They are ridiculously expensive compared to the UK. Maybe Ivor Tiefenbrun and Julian Verkeere are both direct descendants of George III and it's revenge for the loss of the colonies?
I hope that helps...