Mahler vs. Strauss

I never warmed to Richard Strauss. Even though he stated that he could describe a teaspoon through music, I find it hard to listen to. Add to that fact that he was a deadbeat and anti-Semite, I would rather concentrate on other composers.
Mahler, on the other hand, was a more 'human' composer. His later works are pretty deep, but when you open your mind, they are quite beautiful.
As far as how they reproduce on stereo systems, I would say that is listener dependent.
Bob

Mahler became a quick favorite for me during speaker auditions because of the amount of space in the soundstage -- not sure if that captures what you're hearing, but I can glimpse what makes Mahler's orchestration more demonstrative of a deep or wide soundstage. I've not done more than skim this, but possibly of interest

I have always found  symphonies, regardless of composer, are difficult to reproduces on a home stereo.  Have tended to stay with works ranging from solo, up to quintets.  Personal preference I understand, but for me the listening enjoyment is greater.  

I have not really noticed what you're obviously hearing.  I think newbee's possible explanation makes a lot of sense to me.

To be sure, there's a good deal of Richard Strauss I like.  I truly love the Four Last Songs, the opera Ariadne Auf Naxos (some utterly sublime tunes!) and at least the opening fanfare of Thus Spake Zarathustra.  But yeah, I ultimately find him a little bit pat, noisy and empty. 

By comparison, Mahler conjures up universes you can walk around in and get lost inside of.  He can take you back to the dawn of history, to the first days of our planet. His Ninth Symphony takes you forward in time to a day where the earth is a smoking, poisonous ruin.