A screen reader user I know has her own preference and it annoys her when someone adjusts the voice, tone or timing with CSS. It doesn't make the site any less or more accessible adding aural commands but from experience it's something best left for the software to dictate.
Only people using web readers will ever notice any voice styles you apply and they probably have their styles defined exactly the way they want them on the basis that very few sites try to set their own. No one else will ever know they are there.
Originally Posted by Site Accesibility Information
The site does however use a aural style sheet (which can be disabled from your Web browser) that tries to make the sites layout a little better for aural browsers. This includes some mild styling of headings and navigation menus. To make them easier to separate from the main content.
If your using an aural Web browser this Website has left almost everything to be user defined. This is because you should have a voice and reading speed you are comfortable and familiar to.
That's precisely what I'm saying; leave it be and let the user decide.
As for the statement afterwards that you highlighted, most screen readers can very efficiently tell the difference between headers and content if they are marked up as such. To increase and decrease pitch for headers and content to be more distinct is pointless. If you must adjust the aural properties, then do so but may I recommend you leave the content alone as this is the part of the document the most amount of time is spent listening to. I'm sure SR users can forgive a few altered headers.