I've just set one of these up today for my cousins 2 fancy goldfish (2nd hand one with no rubber grommet on 1st section) that previous owner had warned the filter was knackered.
I too binned the carbon/cotton wool/black sponge inserts but kept the noodles.
I took out the grill and placed some of the noodles at the very bottom of the section, taking care to allow enough space in the centre to allow the grill to be replace right at the bottom, then put in the divider. Then I placed the rest of the noodles in the first section and on top of that I placed a piece of black pond filter sponge (which cost me £5 for a shedload - green, black and white large sheets). In the 2nd section I placed a cut to fit green pond filter sponge and on top of that a cut to fit white sponge. I topped the white sponge up with some filter wool which over hangs into the return section.
I then started filling the tank by pouring the water into the filter slowly to wet the sponges and filter wool and pushed them fully into their sections.
After a couple of buckets, got sick and filled the rest of the tank directly. Attached the spraybar and turned on. Because the outlet is submerged I can't tell the flow rate but its by no way knackered and it producing quite a bit of oomph even accounting for a small ammount flowing back ontop of the powerhead but 90% is flowing in the correct direction.
Just realised I've written War and Peace but I hope the description gives a good idea
Based on my experience and assuming the water is leaving the spraybar at a quick lip, I would reccommend completely empyting the trays and grill, doing a thorough clean and replacing the aqua-one inserts with pond filter sponges from a garden centre cut to fit (Even if I was going to replace the sponges every month - which I'm not - I'd estimate I have enough sponge to last 2 years).
You could empty the trays and run the filter to check if the water flows as expected - if not then it may be that its not level and gravity is forcing the water out the powerhead end.
My daughters Endler/Betta/shrimp tank is one of these tanks and I have used the same setup in her filter with no problems for last year with no ill effects with the only filter maintenance being to replace the filter wool when the flow slowed (4 times in a year).
Just realised I've written War and Peace. Apologies