I've had my 8900 just over 12 months. At first I nearly went mad with fmq - breaks and skipping. Then I got some Janome purple tip needles - end of problem.
Seems that the machine "bedded in" as it were, because after a couple of quilts, I returned to other needles. Have just finished a couple of heavily fmq'd quilts with J. titanium 70/10, and Aurifil 50 wt.
I've not done anything with bobbin tension, just have the machine on 'auto'.
But I have found that it will not use Schmetz needles like my 6600, only Organ (who also make the Janome needles).
There is a very slight difference in the length of the two brands - Organ needles marginally longer than Schmetz.