First there are two ‘types’ of subwoofers. Those that are suitable for HomeTheater (HT) or those which are more ‘musical’. You can go to YouTube and find many audiophiles that talk about Subwoofers.
I’d recommend Nemo Propaganda (Now Nemo Audio Project) He has focused on subs and has pretty much covered a very wide range.
While the RS520 does have eARC, its not what I would consider my first choice for a HT. I’d look at an AV Receiver that handles multiple channels.
The RS520 doesn’t have a sub out. This is ok.
Those AIOs or integrated amps that do, will either have a permanent filter at 80Hz, while some have a switch that will allow you to choose a set value like 60,80,120 or something like that. What happens is that you have a low pass / high pass filter where your speakers play from 80Hz and up while the subwoofer will play everything below 80Hz. While this can be convenient there are some reasons not to do this…
On the RS520, you can output to both the speakers and to the line out. You can either hook up one or two subs to the line out. Some subs like the REL can take the output from your speakers and use that into their amp. Here you can ‘piggy back’ on your existing speaker output. REL does this and it is their recommended method of connecting the sub.
In terms of picking a sub… there are many options. Depending on your main speakers you will probably want what they consider a ‘fast’ sub.
@ovanoudenhove said it best :
> When I write fast, you should read it as : controlled, accurate, fast switching. Like f.e. transistor switching. Songs with different deep notes, layers of deep notes playing all at the same time … on a “slow” sub, they will sound muddy, on a fast sub, you will hear the different low sounds and they will be separated well.
Slower subs tend to be integrated into Home Theaters. ‘Fast’ subwoofers tend to be integrated into music systems.
While there’s a character here who doesn’t like the REL, it is actually one of the better subs when it comes to listening to music. It is fast and pairs well with speakers that have AMT tweeters. The REL is very easy to place within the room and depending on the model you can get down into the 20’s. Most music is 30Hz and above. EDM tends to be the exception. In room response will vary.
I run my RS520 w Mon Accoustics Mini s, and a single REL t/5x for my office which is roughly a 10’x12’ room.