I am building a mic preamp based on the 990 amp block. The 990 likes to see 600 ohms.I have heard the 1538xl and was wondering if that will work or if you have any other suggestions?

For such a low input impednace would suggesth the LL1570 used 1:2. The LL1538 are ideally used with amplifiers with around 5k optimum source impedance.