Subwoofer Question

With the help of many in this community I have put together a two channel system I am very happy with. I am a proponent of both vinyl and streaming so the setup is as follows:

Plinius Hiato Integrated Amp
Dynaudio Contour S 3.4LE speakers
Martin Logan Balance Force 210 sub
Dr. Feickert Volare turntable with Jelco tonearm and Lyra Delos MC cartridge
Innuos Zenith server
Lumin T2 streamer/dac
Bryston CD player (don’t use much)
Analysis plus copper speaker cable and interconnects 

The ML sub was something I bought to augment a pair of Magnepan 1.6 speakers before I revamped everything. Quite frankly I didn’t know what I was doing; the thing is huge, difficult to position and I’m not sure I’m getting the bang for my buck.  It gives a boom for sure but is a bit muddy and I don’t have a lot of good positioning options. It just feels like it is too much and not a fit with everything else. My listening room is fairly small and I sit about 10-12 feet away from the speakers.  Because this hobby induces a never ending need to upgrade/tweak I have been thinking about replacing the ML with two smaller subs such as the REL T/7i’s or T/9i.  I do like bass so I feel I need/want a sub. In my research I also keep reading that subs make the midrange sound better if you have the right setup.
Am I crazy? Would very much appreciate thoughts and opinions.

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If you want subs that help to reduce the boomy muddy factor of the ML sub, REL's are likely to help that aspect of what you hear in your room. I was definitely impressed at how different a pair of REL sho/3's sounded vs one JL Audio F112 in my room. Not to say the JL sounds muddy or boomy, but it definitely emphasizes different aspects of bass reproduction vs. REL's character. It is true that a good quality well integrated sub increases the sense of realism in frequencies other than low bass. One gains a greater sense of the space that the music was recorded in. All that said, proper placement is critical to getting good bass reproduction. 
I don't believe in absolutes in audio, but I'll provide my opinion. If you don't have room treatment, that's where I recommend you start.  I've owned HSU, Martin Logan Depth i, SVS 15&16 Ultra, JL Audio F110 v2 with the JL Audio CR-1,  JL Audio F112 v2, and now I have dual REL Carbon limited subwoofers. For HT I prefer JL Audio. For 2-channel I think REL provides different shades of bass that the other subs didn't. In my system REL has the greatest impact on the overall sound, improving everything across the audio spectrum. 
Hey OP:
As you may have seen, to me the issue of integration of a sub is critical.

The sub must integrate to the speakers at the top of it's range, and the room everywhere else.

So, I strongly suggest before you start to talk to GIK Acoustics regarding room treatment, especially bass traps. This may solve your problem with your current sub, and make your current set up sound a lot better.

After this, consider a subwoofer only EQ. If you don't like that idea, then get your two REL subs, but I would strongly encourage you to make your room more speaker/sub friendly with room treatment if not already.

I have been thinking about replacing the ML with two smaller subs such as the REL T/7i’s or T/9i. I do like bass so I feel I need/want a sub. In my research I also keep reading that subs make the midrange sound better if you have the right setup.

Don’t replace, but do add the two. Even better, add three. The problem you’re having isn’t so much the sub being ML as that its just one sub. With only one you’re forced to move the damn thing around trying to find the one spot where the magic happens and the bass is extended and smooth. But the magic never happens. Never can. Because, physics. No matter where you put one sub it will always result in lumpy uneven tubby bass that never goes as deep as you want but thumps more than you want.

The answer is lots of subs. The more subs you use the lower each one can be, you be able to turn the ML down a lot, and this helps reduce boominess. Also with more subs you can set it to roll off lower, maybe even completely eliminating any output in the boominess range. Another thing that helps is they go different locations so create different modes in different places and at different frequencies. Finally you are not relying on one alone to extend really deep. These things all add together to result in much smoother, deeper and more articulate bass than you could ever get with just one sub, EQ/GIK regardless.
Have you, or are you able to, run the Anthem Room Correction software on your ML Sub (labeled PBK)?  If not, you haven’t maximized the potential of what that woofer can do.  Running the Room Correction will make a shocking improvement by helping it integrate better to your room and blend more seamless with your speakers.
I haven’t done the room correction. I seem to remember you needed a PC and it wasn’t compatible with a Mac but I will check into that.

I just checked and the software is available for Mac. I will get the kit and do this.

thanks for the suggestion @cbrents73
nothing wrong with the subwoofer- i believe the issue is that your main speakers have very extended bass output- down to 35 hz less 3db. This is the "F3" frequency (where bass response is 3 decibel down from the rest of the audio range). The "F3" frequency is typically the starting point for subwoofer crossover setting.
Setting the crossover so low means that the sub will not have much contribution - few musical passages have output this low.
If the crossover is set higher, then you will have lots of issues because the signals will overlap, not be in ideal phase or timing, etc.
I had this same problem and despite the best integration tuning with measurements, positioning, crossover and phase adjustments, ARC room correction- in the end I could not get the system to sound great most of the time and I got rid of the subwoofers.
Room correction software will adjust the frequencies but not the phase issues.  
The only option to get this to work was to filter the bass from my main speakers with an additional crossover- say cutting them at 80 Hz for example instead of letting them run full range. This might be a option for you but I chose not to.
My successful option was to run a more powerful amp to drive bass through my main speakers. Yours is certainly up to the task.
The other option is for you to set the crossover on the sub to 35 hz and be prepared to enjoy the occasional really deep bass notes.


avanti 1960 is spot on in his post and and particularly about ARC as it will not deal with the phase. 

However, as an FYI and bit of a plug, many new subs from ML and Paradigm that use their new App Control capability will actually deal with phase and polarity allowing you to adjust it from the seating position.  

Since I work for Paradigm & Anthem, I will toot our own horn in that realm since ML gets their technology from us and our woofers that we make in Canada have two US patents.  I don't want to get into a dissertation about that, but I will also mention that Anthem's STR Preamp and STR Integrated Amp when using the new ARC Genesis Software will measure and correct for phase when using one or two Subs in either Stereo or Mono.