I have used 40s and 40.1s both professionally and domestically for a number of years. For sheer absence of colouration (i.e. the ability to reproduce the human voice in a believable manner) I am unaware of other box-speakers as capable.
The idea that 40s are somehow incapable of reproducing rock music is bizarre nonsense, save two caveats. First, that M40s, while capable of playing at levels that I find unpleasantly high, have been designed to operate well below this point so you may well find the bass (and to a lesser extent, top) too great at high volumes: this is a function of the human auditory system combined with the
equal loudness contours, not in any way a design weakness or oversight. Many speakers designed with the rock'n'roll lifestyle in mind have been balanced to seem 'right' at 95dBA+ but, contrariwise, such speakers are likely to sound thin at more 'normal' listening levels.
The other point (that follows on from the above) is that you are dealing with a very well-balanced, revealing studio monitor that may not be overly kind to some material - but that is its purpose in life. I've seen it argued here and there that a speaker should, desirably, be more 'musical' and thereby make everything sound lush and lovely. I have heard speakers whose owners (and manufacturers) make that claim only to find them not unlike listening under a warm duvet on a cold winter morning - pleasant and cosy, but shielding the listener from reality.
If, OTOH, you are happy listening to rock music at levels generally considered compatible with domestic harmony, you will find a great friend in the 40.1 because it will render all kinds of detail of which you may not previously have been aware - stuff that would not normally become apparent until you listen at levels which, if subject to noise at work regulations, would limit you to about 15 minutes exposure per day!
Incidentally, I have used 40.1s in conjunction with a Quad 909 with great success. It has balanced inputs and is ideal to feed directly from a line-level professional source.