A signaling system supports main and auxiliary communication channels between integrated circuits in the same direction over a single link. An equalizing transmitter applies appropriate filter coefficients to minimize the impact of intersymbol interference when transmitting the main data over a communication channel. The transmitter modulates at least one of the filter coefficients with the auxiliary data to induce apparent ISI in the transmitted signal. A main receiver ignores the apparent ISI to recover the main data, while an auxiliary receiver detects and demodulates the apparent ISI to recover the auxiliary data. The auxiliary data may be encoded using spread-spectrum techniques to reduce the impact of the auxiliary data on the main data.