I have my simple setup (DAC/preamp/DSP and two mono-blocks) on a single shelf that is spiked to the floor between the speakers and about 4 feet from the front wall. Bass pressures build up along surfaces, but especially in the intersection of walls or walls/floor, so best to avoid. This setup also allows for short and equal length cabling.
Previously used a very small rack along center of front wall, but soundstage has improved with this new setup.
Note that I listen with single driver speakers near-field, have a well proportioned room (8 ft x 13 ft x 21 ft), use six GIK 244 panels at front/side wall first reflection points/front corners, and EQ below 250 Hz.