Although I agree that micing the amp is the best (and normally I will use two mic's).  I did a recent recording session and connected our lead guitar player through my POD X3 (I don't remember which "tone" I used).  The lead guitar player is a "must have Fender guy" with an old USA Fender Strat with blue Lace Sensor pickups and the model with the "ball bearing" nut and a 60's Deluxe Reverb amp.  When he heard the final of the CD project he commented that "I made his Strat sound very good".  The recordings were pure "traditional country" with no overdrive/distortion.  The only thing I added to the dry POD X3 sound was some delay using the Echoplex in the POD Farm 2.   

Any reply written in such large red text is worth sitting up and listening to so, as I have no education with power/loads/load-dumps, I need to pick your collective brains on a few related subjects:
 
On the back panel of my Twin, there is a jack called PRE-AMP OUT
The manual states "The PRE-AMP OUT JACK, in conjunction with the POWER AMP IN JACK, provides a post-reverb patch point at the power amplifier input. This jack can be used to provide an unbalanced, line-level signal (1.3dBV) for recording and sound reinforcement consoles, and for driving external power amplifiers, or another TWIN used as a slave amp."
This is the output that I had connected via patchbay to my PC soundcard and gave me a great recorded sound.
I can use this WITHOUT unplugging the big amp speakers but I unplugged them anyway to reduce the sound level in my house. If necessary, I can keep the main speakers connected but I'll just have to soundproof the room a bit.
 
I also have 3 output jacks for speakers: i) MAIN SPKER, ii) EXTERNAL SPKR PARALLEL, iii) EXT SPKR SERIES
The 2 big speakers (8 ohm each) plug into i) and the Impedance selector switch is set to 16 ohms.
I'm kind of assuming that if I try connecting any of these directly to my soundcard then I'll be looking to buy a new soundcard (and possibly a new pair of trousers).
 
There is also an XLR output called BALANCED LINE OUTPUT 3db.
Amongst other things, the manual states: "If the BALANCED LINE OUT is used as a send to a mixing console, it
 
Lastly on the back panel, there's a switch that flips between Output Low and Output High.
The manual states:
 
 

Hi Frink,
 I believe we have already given you the definitive answer. Your amp does not have any load protection for the output transformer except the speakers. If you don't want to use the speakers... you need to hook up a suitable load.
 
 I am offering this advice on the assumption that you own/operate a variant of the Fender Twin known as "the Twin", which has all the features you have described:
 

 
... you know what they say about assumptions. :-)
 
Having read your post, I think you understand what all the options are, so it seems like it's really up to you to decide how you want to manage your choices.
 
I know why I no longer have any Twins... they are so darn loud. :-)
 
The 25 watt option may be a good choice. It's a relatively new feature compared to the classic Fender Twin circuit and it seems like it is a strategy that starves the power tubes of voltage while leaving the preamp tubes at full voltage so it should alter the tone, head room and distortion character of the speaker output substantially, but probably will not alter the sound of direct out options to much.
 
Tom Deering recommended some good power soak products. You may enjoy those choices.
 
You just have to decide what's best for you.
 
I'm glad you saw the big red letters... my primary interest is in helping you not destroy your amp, and I will leave the tone quest for you. :-)
 
all the best,
mike

Thanks Mike,
 
Your mail confirms that I do indeed understand what's going on now - many thanks for that.
 
As an aside, I've just been in contact with a helpful chap at Fender UK and he has recommended a couple of models of load dump such as THD Hotplate which he is using to test amps at full power without disturbing the peace.
 
In any case, I now have options to try - most importantly I know that my gear will be safe.
 
Thanks again for the advice (and everyone else who chipped in).
 
Frink.
 
PS: For the record your assumption was indeed correct.
I do know what they say about assumptions: they make an 'ass' out of 'u' and 'mption'.

Also like to thank Mike and Deering. Very timely warning!
 
Hotplate, hmmm?
 
Will it keep my coffee warm while tracking?

You're right - I'd missed the thanks to Mike and Deering: great info guys- I appreciate your support - particularly as it may have saved my equipment from extinction!
 
Looking at the price of the hotplate, I probably wouldn't be able to afford coffee for a while (on my budget) if I bought one so I looked around and found this:
 
http://www.ratvalveamps.com/dummy-load
 
The chap at RAT has been spot-on with some quick replies to my mails as well - good customer service there.
 
I've decided to spend the weekend experimenting with sound levels in the lab and then, probably go ahead with a RAT Dummy Load if I still want to turn the speakers off. Will report back if anything exciting happens...
 
Cheers,
 
Frink.

Hi All,
 
For the record, my Twin has an XLR output called BALANCED LINE OUTPUT 3db.
Taking a line from here to the soundcard via a compressor gives a really hot signal so, with the OUTPUT switch set to LOW (25w), I can record some good noises and leave the speakers plugged in.
 
So far so good...
 

Glad to hear you got a handle on your tone, Frink!
 
I bookmarked the rat valve site, I just might have him mod my Marshall, the lack of a Master volume has me back and forth with the DSP mixer and Sonar, when I should be laying tracks.
 
Thanks for the feed!