I've done some looking through the literature, and have found the following, possibly useful pieces of information: 

- Component A is O9.5 V
- Component B is at a separation of 0.2 arcsec and has a magnitude only 0.8 larger (HR catalog) or 0.5 larger (Howarth and Prinja, 1989) than comp. A. 
- Howarth and Prinja adopt the following parameters for the star: Teff = 33000 K, logL=4.9, R=7, M=25
- They find  a max. edge velocity in the UV of only 1250 km/sec and infer V_infinity = 1060 km/sec from that. They find Mdot ~ 8e-8 Msun/yr
- Using CAK theory and Abbott's (1982) tabulation of CAK parameters, I find theoretical V_inf ~ 2600 and Mdot ~ 3e-8 Msun/yr. 

With the wind having such a low density, continuum attenuation of the X-rays should be negligible.  

The ISM absorption line measurements of Welty and Hobbs (2001) indicate N_H ~ few X 10^20 (consistent with the value you used for your spectral fits).