Muffled vocals

I seriously doubt this is a source issue.  If I were you I'd attack the problem directly.  Find a way to borrow another integrated and pair of cone speakers and swap them one at a time.  If either solves your problem you have your answer.  My first thought was that that this sounds like it's being caused by some unintended digital room correction or, as others have mentioned, a phase inversion issue.  Changing equipment and re examining wire connections (which you've already done) will obviously rule out these possibilities. 

Then again this could be a perception issue since you don't listen to vocal recordings as much.  Do ALL vocals sound like they're "in back?"  By "in back" do you mean they sound physically behind the instruments or that they sound lower from a volume perspective, or both?  Some speakers are designed to put you in row three of a performance where things seem to be more right in front of you, and others put you further back so you "see" the performance as a whole in the context of the venue and the sound typically comes more from behind the plane of the speakers (I suspect your Tylers are more the latter).  When you move the Tylers closer to the back wall do the vocals sound any better to you?  If you put on something like a Diana Krall studio recording and she's not front and center you definitely have some other issue.  Anyway, hope this helps in some way and best of luck!

Both mofojo and I asked about the digital out of the Marantz cd player. The cd player has a very good dac, maybe the digital out is a weak link. You should try using the analog outputs of the Marantz into the amp. 

I was thinking the opposite. The Lyngdorf is all digital. If you send in an analog signal it will re digitize it. 

The Marantz CD6006 is a fine player for the money. It's the last place I would start to get vocals forward. Imaging is affected by phase response and the CD6006 has excellent phase response. The player uses the audio circuitry from the much more expensive units. It maybe just a tad lacking in absolute smoothness, but overall it is excellent particularly in creating a realistic sound stage with capable equipment. 

It appears the Taylors may be partially time aligned, but this may not result in minimum phase error. I imagine they will have a small sweet spot both horizontally and vertically due to the upper woofer.

Given the speaker is about 60" tall, ear height should be about half that to minimize smearing between the woofers. A good portion of the male vocal range may be reproduced by the woofers and the unequal path lengths and reflections could be the issue.

It would help to know your room size, openings, floor treatment, furniture and equipment position.

cal91:  I, like you, have a comparatively basic CD Transport. (wow, I really needed that comma after the 'I', huh?). It wasn't until I purchased a good Dac that I began to enjoy listening to my CDs.
The sound just bloomed; sound-stage, detail, vocals, positioning.
I did have to adjust the room and the speakers for a while to make the sound-stage really wide and deep. I do have an inexpensive tube Pre which probably helps, but the biggest change was getting a good, musical Dac to play the transport thru.
Hope this helps.

Dave