Digital sound is fine, but analog rolled off Why?


My set up is Oppo CD-player->Music HAll Maven(ClassAB at 100W)->ATC SCM12 speakers.

When I listen to CDs I am pretty happy with a sound, but once I switch to LPs: Rega P3->Denon DL-160 cart.->Rotel RQ-970BX Phono stage my sound looses stage and it seems like treble as well as bass are rolled off. Adding volume does not change the quality of the sound at all.

I tried the same analog combination with easy-to-drive speakers of the same volume and analog sound became much more open and alive/present than with my ATC speakers.

I am puzzled : I know on one hand that ATC speakers are very hard to drive, but I lack engineering knowledge to conclude how is it possible that digital source produces decent sound and analog source drops in quality?
The only idea I came up with is : My phono stage does send enough information to my amp for easy-to-drive speakers, but that information gets lost when I switch to ATC SCM 12s.
Any ideas why this is happening? Could speaker such as ATC kill analog sound in my system?
128x128dkzzzz
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"Assuming stylus and cart and cartridge alignment is in good shape, I'd check into the impedance matching from cart to phono and phono to pre-amp as Tvad suggests as a likely culprit.
Mapman"

How do I check for impedance between components? Do I need some electronic meter?
Would impedance mismatch explain the difference in sound between easy and hard to drive speakers?
You may also want to play with the VTA adjustment of your arm, even if it requires obtaining Rega's spacers to do so. The effects that you describe can be caused by VTA maladjustment: (http://www.psaudio.com/ps/how-to/how-to-adjust-the-vta-of-a-turntable/) Note what this site recommends you listen for as an indicator of proper VTA adjustment.
On your phono stage is there any adjustments for resistive and capacitive loading for your cartridge;maybe give the manufacturer a call to see what he may suggest.
I think tvad and mapman suggestions are correct.
As Thorman says: are your turntable and tone arm properly set up? Is your cartridge aligned correctly?

What happened to digital sound when you tried the easy-to-drive speakers?
Assuming stylus and cart and cartridge alignment is in good shape, I'd check into the impedance matching from cart to phono and phono to pre-amp as Tvad suggests as a likely culprit.
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Try borrowing another phono stage if possible...That will at least tell you if its your current phono...I wouldn't think it would not be your speaker,if they work well with Digital...Could you possibly need to re align your cartridge set up???