Bass management--high/low pass filtering

@bimmerlover   Your speakers have triple 8" drivers for excellent bass resonse.

 24Hz (-10dB); 26Hz (-6dB); 35Hz (-3dB)

By crossing at 80hz. you cut them off at the knees. Why buy a speaker this capable and then put a choke on them? I'd bet the triple 8" drivers produce BETTER, tighter mid-bass in the 35 to 80hz range than your subwoofer.

It's called a "subwoofer" for a reason. To lift the line in the sub region. For you the sub would come in around 40hz. It's NOT a woofer. You have triple 8's for woofers but instead your asking the subwoofer to handle this mid-bass range and hobbling the very capable triple 8" drivers. Why buy them if you don't use them?

@gdaddy1 if you know anything about logarithmic scales, at -10 dB it has dropped to a meaningless sound level, so has essentially -6 dB.

The F328Be:s taper out at 35 Hz at -3 dB, which is still a meaningful sound pressure. One of my subs, the KEF KC92, goes down to 11 Hz at -3 dB, a huge difference, and I low-pass filter it at 100 Hz.

In addition, the tube power amps are not that great in controlling the lowest bass as they have a relatively low damping factor. I trust the sub's 2x 500-watt solid-state amps to do a better job controlling the bass drivers.

Besides, I picked 80 Hz, but anyone can choose their preferred high-pass frequency. It is, after all (still, but unfortunately in peril) a free country.

@cooper52 I have an suggested experiment that you could try. Your integrated has both pre-outs and HT-bypass. So, you could send the signal from the integrated’s pre-outs to an active crossover, then at the crossover, fork the signal, sending the higher frequencies back to the integrated’s power amp (via HT-bypass) and the lower frequencies to your subwoofer. 

Options for your crossover include Sublime Acoustic’s K231, maybe a MiniDSP, or a JL sub crossover. 

My experience. I’ve heard a JL crossover + subs in a buddy’s system. I think it sounded great. I haven’t heard the Sublime unit--I’ve only seen OCD Mikey recommend it on his channel as a solid contender for the money. 

I’ve done what your describing with my TV system. In my TV system, I currently use KEF LS50 Wireless II’s, which have their own internal DSP engine with both high and low pass filters. I paired them with a REL HT sub. I had initially tried the crossover at the speaker’s -3db point (45hz) and at 70-80hz (often recommended in HT situations). I left the crossover at 80hz to live with for a while. Then, one day, I found someone’s charts showing when the LS50 speakers distorted across the frequency spectrum and at different volumes. I don’t recall the exact chart figures, but each chart showed distortion across the frequency spectrum when playing the speaker at different volumes like 80db, 85, 90, 95, 100, 105. What I saw in these charts was that starting at some volume, say 90db, that all frequencies 100hz and below were above some distortion percentage while frequencies above 100hz were not distorting. Charts at higher volumes saw a greater distortion asymmetry across the frequency spectrum. From that information I hypothesized that I should try handing off all frequencies below 100hz to the sub to see if I noticed any change in the sound. I went into the KEF software and changed the crossover to 100hz, and even though I wasn’t listening at 90db, the system sounded more effortless. (I also tried setting the Xover to 120hz, and that sounded equally effortless to me.)

Still today, I have this hypothesis that (1) some systems can benefit when offloading frequencies to subs typically handled by the speakers, that (2) crossing the subs over higher than usual (higher than 80hz) can be effective, and that (3) that a good setting for the crossover is the point where your specific speakers begin to distort asymmetrically across the frequency spectrum. 

If you get into JL’s sub integration philosophy, you’ll learn that they’re big proponents of offloading low frequencies from the mains, and of crossing over at higher frequencies, even for expensive speakers that are "made to play full range." But, I haven’t seen JL articulate where to set a crossover at. Anyway, audio is an experiment, and in experimenting with this philosophy, you may find a solution that works for you. 

Marchand Electronics makes a variety of high pass filters and crossovers designed to limit the low frequencies going to the mains. While my mains are very capable down to 40hz, my room acoustics favor the low frequencies near the floor rather than 30 inches above, where overall things sound best. It's not a matter of philosophy, it's listening and creating the right system for your room and tastes. 

As for using a sub for below 40hz, you'll find very little musical information there. Few instruments produce frequencies that low. Its great to have it available but its not something you're going to hear often.

But by using a sub for below 80 or so, you have a speaker specifically designed for those low frequencies rather than a woofer that is expected to produce those as well as much higher frequencies. 

@bimmerlover 

if you know anything about logarithmic scales, at -10 dB it has dropped to a meaningless sound level, so has essentially -6 dB.

The F328Be:s taper out at 35 Hz at -3 dB, which is still a meaningful sound pressure. 

Exactly my point. You want the subwoofer to pick up that lower range. Those speakers do 35hz and up really good but you're not going to let them do their job. So, why did you buy them? Because they look impressive but you're only going to use half the drivers capability? Makes no sense to buy something and not use it because the tube amp is mis-matched to the capability of the speakers.

FYI... bass in music lives in the 35 to 80hz range where your speakers are optimum but your amp is weak.  

It's your system and you are free to set it any way you want. However, it's not good advice for everyone and could hinder more than help.