Been thinking about this some more, and had some additional ideas for you to chew on, inspired by the lack of proper bass management in your front end and limits on what you can tweak because of that.
The first thing that came to mind are potential risks to your speakers from high spl playback of bass heavy content. Your Perlisten mains are a ported design. I'm not sure how much you know about how the hole in a box works, but briefly, below port tuning the drivers and ports will go increasingly out of phase and decouple from each other. Of specific relevance to you, if you allow your Perlistens to run full range and the source contains frequencies below the speaker's port resonance it will result in excessive cone motion but no additional output, which will wildly increase IM distortion (that cone motion will modulate all higher frequencies that the woofers also produce) and risk damage to the drivers by exceeding mechanical limits. Now, as I alluded to upthread, this probably only matters if you're really cranking it. But it is the nature of the beast with reflex loaded speakers. The easy and inexpensive solution would be to use a line level hpf between your preamp and the amps driving the Perlistens, creating a protective "rumble filter" but otherwise allowing the Perlistens to dig as deep as they can. An outfit called Harrison Labs sells them, they're called "F-mods", and they come in a variety of different values (to effect different hpf cutoff frequencies) and in both rca and balanced flavors. The cutoff freq are a function of the f-mod values and the input impedance of your amp. The appropriate value f-mods would allow your Perlistens to run down to their native roll-off, and reduce potentially harmful frequencies below that. F-mods do exactly what they claim to, and add zero noise or distortion, as confirmed by Amir over at ASR. They cost about $30. Cheap insurance for your kick ass Perlistens.
Next topic, the subs. Few subs these days cater to us luddites with two channel rigs trying to add some subwoofage. The Arendals you're looking at are feature laden, but they lack any sort of hpf on their line level outputs, they're just pass-through (thus the suggestion for the f-mods). Many subs, including the Arendals, have built in dsp, which cause a teeny, tiny bit of latency. Your upstream kit lacks the ability to compensate for that. Now, that latency may or may not be an issue. If it is, it will make blending the subs more challenging. Solution? Place the Arendal or similar subs closer to the mlp. That may not be an option though. Alternate solution: consider subs that don't have dsp, e.g. Hsu subs, that don't exhibit the latency of dsp equipped subs. Such subs could be placed more in line with your intended placement (diagonally, or otherwise out on the periphery of the room). Along with placement considerations, it would involve a trade off between easier integration on the one hand, and potentially beneficial features that dsp offers such as PEQ on the other.
I mention that second point based on my own recent experience replacing subs in a retro two channel rig essentially similar to yours.
