Yes, the FX5 is one of those devices that you just can't leave alone and begs to be modified. I wanted to make a couple of comments about statements on the website.
First, the Fluval corrugated tubing is a dream to work with compared to thick-walled, noncompliant pvc tubing and I personally prefer it. I too have pondered the issue of internal turbulence and resistance due to the lack of internal smoothness. However, I would guess that within a few months, the striations fill with sediment and biofilm and greater smoothness is generated.
It's true that the filter intake doesn't have much "suck" and I've also witnesed particulate debris wafting by without getting pulled in. However, I view this as a significant benefit. Having bare bottom tanks, this allows debris to collect on the bottom of the tank, where I can siphon it out. If it gets sucked into the filter, that just means that I have to clean the foam pads more frequently.
Finally, does anyone know if the circuit board will turn off the motor if the impeller freezes? IMO, the temperamental "smart pump" technology, which monitors the pump output is the Achille's Heel of this filter. Frankly, I'd like to investigate disabling the entire circuit board.
BTW...nice job on the website.