Hi Oscar,
A few points to start.
Try starting the process without any 'old brown'. The developer will last a little longer and you will be able to see how the print changes as the fresh developer exhausts. An initial print may be ready to pull at 5 mins but a third or fourth print may not be ready until 35-40 mins and will display more pronounced lith effects.
Not all ADOX paper displays lith effects well, or at all. I have achieved the best results with ADOX Vario Classic G. This displays good infectious development and a warm tone. It exhausts the developer quickly.
I suggest you invest in some FOMATONE MG. This quickly produces lith results and is economical on developer. This paper will certainly produce pinks and browns.
Modern papers are less inclined to produce colourful effects straight off, which I suspect is due to the manufacturing process being 'cleaner'. You can achieve a lot by developing paper in a standard warm tone developer, then bleach and redevelop in lith. This has the advantage that the lith process is in daylight and it's easier to judge when to pull.
I suggest you also try Moersch Easy Lith
Think about joining the Lith Group on this website.

Cheers

Simon
5Rise Graphic Art
Bingley, West Yorkshire