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I have the values for this circuit, I guess I didn't think it would matter in determining the kind of load...
L202 22uH
L203 8.2uH
C200 82pF
C201 10uF
R200 560-ohms
Q200 2N3906
The component values tell, that the filter characteristic is a 3rd order chebyshev low-pass with pass band ripple < 1 dB. The input impedance is resistive/inductive over the full frequency range with a minimal magnitude of about 400 ohm. So you shouldn't have problems to drive it by an OP buffer. If I didn't miss something, you didn't yet tell about the used OP type nor about the exact problems observed with it.