Having owned and sold a pair of Fostex TH900's and also having a high end system I would have to say trying to replicate the same sound of the Fostex in any pair of bookshelf speakers nearly impossible ! The Fostex in my opinion are very bright sounding headphones . I did love transparency and the bass but overall I could not keep them on very long, my ears and brain were very fatigued after 30 minutes of listening !
Listening with headphones and listening to a pair of speakers is a totally different experience unless your going to wear those speakers on your head !
The right professional to set up a room and equipment is money well spent and I think a consultation before you go any further is my recommendation .