I had a Janome 7700... and while I liked it, I sold it because I didn't want two 7mm wide machines - the one I have here now is a BL Ellisimo Gold.
The one thing (and call it old-dogs-new-tricks) ... is that the foot on the Janome is not centered to the ankle. This might not bug anyone else on the planet but me... but it drove me crazy after 30+ years with my old ElnaGirl that has her footie centered to the post that holds it.
You can't beat the dual feed on the 7700s... but I never tried an 8900. I'm assuming they should function similarly.
Still love the sweetness of sewing on the BL... so smooth.
All I can say is that you really need to sit down - breathe - and be alone with each of these for about 30-45 minutes with fabrics and tasks from home to compare them out.
They're both wonderful machines... it's going to be a personal preference thing. Have fun!