Oomph or pressure?

I had this same perceived problem with autoformers and the Lightspeed. A transformer based passive did the trick for me. Some examples off the top of my head are Music First, Electra Fidelity, Silvercore, older Bent Audio units.

is that normal for a passive?

It is a common complaint.

Passive systems, which include transformer volume controls, are a bit too simple to do their job perfectly. That is why you see so many threads about this topic.

If all the parameters surrounding the control are right, it will work pretty good. But getting them right can be a bit of a trick- it depends on the other gear in your system including the cables.

Transformer type controls are different from passive volume controls in that a transformer is used to do the job of volume control- you use different taps to affect the output voltage. The problem is that transformers have to be properly loaded in order to do their job of impedance transformation. The thing is, you're looking for voltage conversion, not so much impedance conversion, and the impedances on either side of the control (source and power amp) are not changing, so its job is made a lot more difficult!

When a transformer is not loaded correctly, it can ring (distort), it may not express its turns ratio correctly and may instead express some of its internal capacitance (which results in non-linear frequency response) and/or it can be rolled off if its load is below what is called 'critical damping'.

For this reason the transformer will need extra switch decks to switch in different value resistors as part of the loading scheme (the source and power amp being the other part of that, and as you might have guessed, its a bit of an uncontrolled variable as amplifier input impedances vary by about 10:1 depending on the amp).

The other part of this is that most people don't realize (including many designers) that the job of an active line stage has four aspects:
1) volume control
2) input switching
3) provide any needed gain
4) control the interconnect cable to minimize its effects on the sound of the system.

It is that last bit that is most widely misunderstood. Most passive systems don't provide any cable control until the volume is turned up (and then the impedance of the source is what is providing the control), which is why you hear a lack of 'oomph' at lower volumes.

IOW, it is quite possible that you can get less coloration with a well designed active line stage.

I have an Intact Audio autoformer that uses the same autoformer as your Emia (assuming you have the copper version, not the silver).  And I also have an Emotive Audio Epifania linestage (modified) which uses a single 12B4 tube per channel.  Coincidentally I have been comparing the two over the past few days for the first time since I got the autoformer last fall. 

In my case, the autoformer and the active linestage sound very, very similar with regard to tonal balance, detail and dynamics.  In terms of tonal balance, the autoformer has a little more weight in the bass and the upper midrange is a bit dark sounding; to my ears the Emotive is just about perfect in tonal balance.  The Emotive has somewhat more refinement and delicate detail in the highs, and it has a more involving, propulsive sound.  The autoformer has a lower noise floor (as in next to no noise).  These specifics aside, on an overall basis the active and passive sound remarkably similar.  

In particular I have not noticed any lack of dynamic "oomph" at lower volumes.  That makes me question whether your source is able to drive the autoformer properly.  I have much experience over the years with resistive passive attenuators and they do have the dynamic reticence that Ralph describes above.  The Emia autoformer does not suffer from that problem.

All of the above is In My Opinion and In My System of course.