It's kind of been mentioned above already, but you'll not get the speaker movement which really contributes to "cranked" tones at anything other than cranked, loud volumes. Of course, you can get the tube distortion on the power amp by the methods above (I really don't need an amp, but I am kind of GASing for a Martamp for home use!). Personally, I like the feel of the speakers really moving some air, but sadly this is just not possible at house-friendly volumes!!
Roo