Re: Marshall Super Lead w/ attenuator and/or master volume mod- good idea or bad idea
Doing this is like using a top fuel dragster as a grocery getter. Doesn't make sense.
If you need close to or bedroom levels, get a small amp or get a modeler. Use something that it is meant to be used for.
I've got a Bugera 1960 Infinium, which is basically a post-'73 JMP 1959 modified like Randy Rhoads had his modified. I run it through a Jet City Jettenuator. It's not only for volume reasons. I do it live, too, depending on how much dirt I want from the amp. This circuit starts to get those classic sounds once the power tubes start to compress a bit.
That said... If you're going to spend the money to get a Super Lead, why not just get something with a lower wattage, like a Friedman Pink Taco.
Or get yourself something from Ceriatone. I'm looking to do the build-it-yourself kit of a Marshall 1987 (JMP50) because I like building stuff, but GuitarAmpUSA.com sells them pre-built for not a whole lot of money.
You could get yourself a Son of Yeti:
http://guitarampsusa.com/index.php?route=product/product&product_id=107&search=yeti
Or a full-size Yeti in either 50 watts:
http://guitarampsusa.com/index.php?route=product/product&product_id=114&search=yeti
Or 100 watts:
http://guitarampsusa.com/index.php?route=product/product&product_id=113&search=yeti
Or if you
REALLY want a non-master-volume 1959 Super Lead:
http://guitarampsusa.com/index.php?route=product/product&path=59_65&product_id=112
Just to note about the prices there, they start with the lowest option, which doesn't include tubes or a head cabinet.
Also, I have nothing to do with GuitarAmpsUSA.com. They get recommended a lot over at TheGearPage.net and they have to be good because TGP likes to rip apart anybody that even sneezes the wrong way which doesn't give them haunting mids and crystal lettuce.