Will a new sub sound better than my Velodyne F1200?

I think one of my integration issues is that my mains aren't high-passed. With the ports plugged, they start to roll off around 80hz but it's a very gentle 5db/octave rolloff at that point, and then there is probably a 12db/octave rolloff around 55hz. There is a LOT of overlap, and both the mains and the sub show a big room node at 60hz. 

Does anyone have recommendations for good XLR high pass for my mains? I don't want the signal quality to the mains degraded in any way.

I'v used the Velodyne F1500 for 25 years for movies.
The F1500 uses a 15 inch woofer and a built in amp.
My system is Canton Ergo 90 speakers, Canton center channel and Canton rear channel.  The F1500 is an amazing sub.   I wouldn't use it for music, but for movies its incredible.  I bought it in 1992 in Harvey's electronics in NY.
I remember Harvey's would play the Infinity SSW-210 Sub which was Infinity's top Servo sub for movies back in 1992.  The infinity SSW-210 used two 10 inch woofers and a built in 250 watt amp. 
The infinity was good for movies, but the Velodyne was superior for movies.  

The only problem with the F1500 and F1200 Velodyne completely abandoned any support for their early drivers that were made in house.
I never heard the F1200, but i know it was the Velodyne sub below the F1500
If its anything like the F1500, it should be good for movies. 
My only regret was i should have bought a backup 15 inch woofer for the F1500. 

sboje if your looking to use the Velodyne F1200 for music, i wouldn't recommend it.  These Velodyne subs from the early 90s were mainly for movies.    

Well, I took a leap of faith and bought an SVS SB16-Plus. In short, it is a significant improvement.

My Velodyne F-1200 sounded very boomy by itself.

With a Velodyne SMS-1 in front of the F-1200, I was able to get the frequency response pretty flat, but things still sounded a little out of sync, or slow.

The SVS has built-in parametric EQ, so the SMS-1 was removed from the system. To tune the SVS, I had the SMS-1 output its test tones into my pre-amp (and therefore through the entire signal chain), and I used the SMS-1 microphone to then measure. I made EQ corrections on the SVS itself. This got me to a pretty flat response, though there is still a bump between 55 and 65hz (big room nodes there even adjusted -8db or so). I then used the kick drum on the Police's "Murder by Numbers" to fine tune the phase on the new SVS sub. I find this results in a better sound than playing a test tone at the crossover frequency.

Now the sound is a lot punchier where it needs to be, and the entire bass range is a lot cleaner. The 16 inch driver may be massive, but it doesn't seem to have any detectable overhang, unlike the 30 year old Velodyne design.

I have a strange room setup with a lot of cubic feet, but I'm not stressing this sub at all. At typical listening volumes, you can't even see the driver move. However, if you crank it up the volume and put on some music with serious low bass, hold on to your hat!

I am running my Revel M106 speakers full-range. I don't know if you can ever get an absolutely perfect integration of a sub and a monitor speaker running full range. You definitely want the sub playing the kick drum, which means there's going to be some overlap and the phase of the sub will only be perfect at one frequency. Nonetheless, I'm really pleased with the results. 

FYI, the SVS has 3 parametric EQ points. If you buy this sub, plan on using one of those to put a low-Q bump at 20hz to get the thing playing flat down into lowest octave and then into the mid-teens. So practically speaking, you're left with 2 parametric EQ points to deal with your room.