¿qué subwoofer comprar para unos B&W CM8?

Esta noche he escuchado un concierto en Jazz y ahora sí que noto un cambio abismal. La parte de música ya lo tengo casi configurado, me ha servido de mucha ayuda el siguiente post.
Curso sobre subwoofers en Supersonido. Grandioso.

Al principio mi configuración inicial era todo small con corte 80 y solo conexión por RCA. Por lo menos con mis altavoces el sonido era no muy bueno echaba en falta la claridad que tenía antes, asimismo en pure direct no me sonada el Subwoofer.
Ahora lo he puesto los frontales en large, he conectado en High level al subwoofer y he configurado el corte en High en 45 . Esto me permite escuchar la música en pure direct con unos bajos muy notables. Os seguiré contando cuando haga más pruebas.

Lo que sigo sin entender para que sirve el Output/lef o in entiendo que es un filtro pero por ejemplo en Highlevel entiendo que no corta el AV sino el subwoofer ¿no sería más correcto ponerlo en in?.

y es siguiente texto sacado del foro de AV forums para este subwoofer.

Texto en Inglés.

Most of the below applies to all AV Receivers, however it may make more sense if you have a Yamaha due to the slightly different ways that each manufacturer names things...

An AVR should connect to a subwoofer via a single RCA-to-RCA cable, from one of the AVR's sub-outs to one of the sub's low-level inputs (which one you use on the sub is usually clarified in its manual). You should set the low-level input filter on the sub to "off" or whatever the highest available setting is.

A 5.1 sound-track will contain a dedicated Low Frequency Effects (LFE) channel, this is what the ".1" in "5.1" is. This track is sent to the subwoofer regardless of any settings as long as your system has a subwoofer present in its settings.

Additionally, the 5.1 track will also contain low frequency data in some of the other 5 channels. If your speakers are set up as "large", the AVR assumes that they are capable to handle all that low frequency information and will send the entire thing (excluding the .1 of course) to them. In the real world, very few people have "large" speakers - they would have to have at least a 10" bass driver to really do justice to the audio mix, and most likely have their own dedicated amplification.

So what actually happens is you set your speakers to "small", and set a per-speaker or per-system (depends on the AVR capabilities) crossover frequency. What then happens is that from the 5.0 signal being sent to your L/R/C and surround channels, the AVR will filter out anything below that crossover frequency, add it to the dedicated LFE track and send it all to the subwoofer (the rest of the signal is amplified and sent on to the speakers). As a rule of thumb, THX standards suggest a crossover of 80Hz however for small satellites that may well go up to 120-150Hz+, and for big speakers you could take it down to 40-60Hz; it's all down to the speakers, the room, your preferences etc.

For simple stereo inputs (2.0 PCM, plain CD's - not SACD!, etc) under a standard output mode, the same filtering will apply to the front L/R speakers, and the bass will be redirected to the sub. In Pure Direct, the full signal will go to the speakers and nothing to the sub - this is where the high-level connection would come in.

High-level connects to the AVR's amplified outputs (the ones that go to the speakers); in this way it's a bit like "extra bass" (see below) in that the full signal will go to your speakers anyway, but the sub also sees it (it takes no actual power from it, just a few mW at most let's say) and will filter it below the "high level" setting on the sub and output just that. You will need to tweak this to find the point where it blends in well with your main speakers, otherwise you'll be putting out a lot of exaggerated bass as it'll be coming both from your speakers and your sub. For the 99.36's, I would say somewhere around 35-45Hz may be a good point for high-level filtering.


Now then, there's another tweak, at least on Yamaha AVR's called "extra bass". If you listen in Pure Direct, then all the below is invalid - it only applies for Straight or the other modes.
ON means that a Large speaker will be sent the entire frequency range; anything that falls below the crossover that you set on the AVR will also be "copied" to the subwoofer output to give you extra bass. You cannot have this unless your front L/R speakers are set to "Large" - they couldn't handle it all unless they were "Large" anyway, right?

OFF means that the speaker will be sent a signal that is filtered so that whatever is below the crossover that you set on the AVR is entirely redirected to the subwoofer. It's a small speaker so it can't deal with low frequencies anyway and they'd just be giving it work that it cannot do - makes sense?

If you have this set to ON (and hence the speakers to Large), then your sub should also be getting bass as well as the speakers. The downside to having the same LFE signals reproduced by both the speakers and the sub is that it'll most likely sound "wooly" / imprecise etc.

Calibration!
Plug everything in (except the high-level cable I'd say), turn the Phase on the sub to 0, the gain to somewhere around 30-45%, plug the calibration mic in and let it do its thing. Once it's finished, you can use a tape measure if you want to adjust the actual distance detected; set all your speakers to small if the calibration thought something else, and post back with the crossover that it figured out; they should be fine really, but we may spot something if it doesn't look right. One word of warning - the sub gain that auto-calibration figures out may be well out, it should be within the +/-3dB range usually. Play with that and the gain on the sub itself until it sounds right to YOU.

Then come back with all those extra questions and we'll be happy to help

ps: if you had a simple stereo amp then all that AVR filtering stuff wouldn't apply, as you could only connect the subwoofer via its high-level inputs in the first place; this somewhat simplifies it all, but gives you a bit less flexibility.

I hope this has been informative, and I want to thank you for reading (I've been watching too many CBT Nuggets recently..).