Since there is limited information (other than some quite possibly unreliable RMAA tests) available on the audio quality of the Auzentech X-Plosion, I am not sure how much, if any improvement it would be, but the Asus Xonar D2 (PCI) or D2X (PCIe) supports 7.1 output, S/PDIF input and output, and has 24-bit/192 kHz DAC and ADC. It is advertised to have 118 dBA signal to noise ratio on all analog inputs and outputs (at the full scale level of 2 Vrms), and very low distortion. I have the cheaper Xonar D1 which I find fairly good other than the lack of a built-in headphone amplifier that the D2/D2X do not have either. If you do not mind basically buying the E9 again, the Xonar Essence ST (PCI) or STX (PCIe) would be even better, but these are limited to stereo (2 channels), and have no S/PDIF input; as already noted, the ST/STX have an integrated headphone amplifier that performs very similarly to the FiiO E9.
Especially for gaming, emu20k2 based cards by Creative and Auzentech might be worth considering, but due to the limited information in the specs and no reliable tests, I do not know how these compare to the Xonars in terms of audio quality. The Auzentech X-Fi Forte has a good headphone amplifier, but this card is reported to be unreliable and prone to failing.