The DNG Converter doesn't make RGB images like TIFs or JPGs that you can view, it typically converts native-raw format to DNG-raw format. You would need to use a raw converter of some sort to view the RGB rendering of the raw images whether those images come from the native-raw format or a DNG-raw format.
What the DNG Converter might be doing is embedding a thumbnail or preview that is computed as the result of the default Adobe Camera Raw conversion parameters which could be at a reduced size, but you really need to be using Lightroom or Photoshop with the Adobe Camera Raw plug-in to create an RGB image from the raw data to judge how well it looks, and then the conversion parameters are up to you to set.
How are you looking at those DNG files to determine their quality?
I do use Camera Raw 6.6 and Photoshop CS5.5. That's when I see that I've lost all of the dynamic range, especially in the shadows when I edit with the DNG.
I look at them side by side while editing in the programs and I can see much more detail in the TIFF.
The Sony converter is reading the in-camera settings for noise reduction and other settings that Camera Raw ignores. And if you are comparing that TIF with an unprocessed DNG file (in other words, you haven't done anything to improve detail and reduce noise) you are seeing what would be expected. The DNG file is a raw file. Anything that you may have done to that file in the Sony converter prior to converting will not be seen. The DNG file is going to be a conversion of the raw data as it was recorded by the camera sensor. Any and all improvements that you want to make to that image are your responsibility. In-camera settings do not apply.
So your issue is you prefer the Sony raw conversion rather than the Adobe default-settings raw conversion? That is not surprising because camera manufacturers are trying to do something automatically that produces JPGs that users like but are otherwise stuck with, whereas when you use a raw converter, you are in charge of setting things the way you want. A Sony raw converter will be able to read things the camera set for sharpness, noise-reduction, contrast, and dynamic-range compression, etc, whereas, while Adobe's raw converter has analogous settings, the Adobe's raw converter is not made by Sony so it cannot interpret any of the Sony-specific settings.
When you say you're losing DR especially in the shadows, does that mean your shadows or all the darker shades have become black or too light and the image lacks contrast in Adobe products as compared with the Sony conversion?
If all the dark shades are getting flattened to black, perhaps your monitor needs calibrating with a hardware calibrator. Do you use one?
If your shadows are too bright or the entire image lacks contrast, then if you're lazy you can click Auto in the Basic toning area, and in addition, upping the Clarity, usually adjusts local contrast and gives the image more pop.
If you are dealing images shot in some special HDR mode in the camera then LR may not know anything about that, and the initial conversion may be off because the camera is actually under- or over-exposing and then digitally enhancing the shot. Adobe will read the actual raw data, which may be too bright or too dim and then you're required to "enhance" the shot, yourself. It is usually better to turn off any auto-fix or DR modes in the camera and properly expose the image, then at least the camera and LR will have a more similar starting point.