mistik,
You are shooting yourself in the foot. You should not mention what you mentioned because it will work against you.
Now that you said you own e-rock.com and have an entertainment company and you are thinking of buying erock.com, the owner of that domain might rise the price considerably. As a buyer you should never look too interested or too desperate because even if the person was ready to sell for cheap, they will rise the price after you explain them that you really need especially that particular domain for a strong reason.
When buying a domain you don't want to say, I must have this domain because of this reason. On the contrary, what you want to say is, I could easily find another domain that will do as well.