I've always love the sound of  a JMP or JCM 800 cranked up through my 412 cabs.  Only problem.  I live in a neighborhood area, and my house is not soundproof.  I was using a version of ISO cabs I built myself (much like the Randall ISO cabs).

 I was hunting for a cab simulator for my ADA MP1 tube preamp I just got back from having the 3TM mod done on it (sound freaking great).
 
 So how do I play my guitar, or bass, or anything amplified through a loud amp head and have no outside sound without burning up the output transformers ?

 I found this little gem in my search for cab simulators.  Kinda pricey but it does a lot of stuff,. tons of cab configurations, mic setups and sounds.

http://www.two-notes.com/boutique/lang-en/hardware/1-torpedo-vb-101-3700673800019.html

 http://www.diffusion-audio.com/xcart/Two-Notes-Engineering/

Two notes is in France I do believe

I did not read the full details of The Two notes gear, but saw the price and freeked out 

So what would the difference be between say a Line6 pod and the above, line 6 being a fraction of the cost?

I use line 6 and guitar rig.. anymore I take my tube guitar preamp ( ADA MP1) and run it into two studio preamps.  Or I record clean through the studio preamps and use line 6, or guitar rig in the tracks plug-in.

  Some peoples ears are very finicky, or precise.  They can tell the difference from line 6,.. to lets say a mic'd JCM 800.   I can hear the difference on my recordings, I'm just not that picky.

 The difference is  two- notes went into a major study of mic'd speakers and why they sound better than let's say a line 6 product.  They were very precise in their copying the speaker reactions and what was the attributes to many different speakers and cabs, (like line 6 did). Then instead of trying to copy or simulate amps and speakers. They let you use your own amp, you can go out of the speaker output  into the torpedo unit.  It has what's called a dummy load, or load resistors, or load plates, that way you don't burn up you output transformer on you amp. Then that signal is brought down into the digital realm for a very precise speaker simulator.

 Benefits of this . 

You can use a tube amp the way you want.  Let's say you have a modded JCM 800. set up to sound like ACDC's sounds.  You can use that amp in you apartment without waking the whole neighborhood up. 

you can use your amp with all your pedals an boost what ever and it is going to sound like your mic's cab.

The other benefit is gigging.  I don't know how many times I have put a mic in a certain location on my speaker cabs, it work in this exact spot for 4 or 5 gigs, then I end up in a venue and no matter where I put the mic,  I can't get the proper sound out of the P.A. .
Serious room problems/ and or my amps volume would be to loud for this venue.. I could take the torpedo unit plug my amp into it, use the settings I like, and take the mic, and whatever problems I'm having with it, out of the equation.

This unit is more for the tube amp purist that what that exact sound his amp has, but has to record, or perform at lower volumes that the settings on his amp would allow (dimed out Marshalls, or whatever amp).