The iFi Micro iDSD has been well reviewed: $500; PCM up to 768 kHz, double DXD, DSD to up 512; USB, coax, and optical inputs; coax, RCA, and variable headphone voltages output options; battery powered; small (6" x 3" x 1").
Audio-GD NFB 28 w/TCXO is another interesting option: $800; PCM 32/384, DXD, DSD; Optical, coax, BNC, USB, RCA, and XLR inputs; XLR, RCA, XLR/1/4 inch headphone outputs; authoritative bass, pristine clarity, slight smoothness/warmth, fully balanced design