The Lian Li site gives these dimensions of the PC-05A
Dim of case 210 x 381 x 490mm (W,H,D)
Dim. of M/B area 188 x 348 x 226 (W,H,D)
Dim. of PSU area 151 x 87 x 168 (W,H,D)
The ATX spec for a PSU is 150x86x140 or 5.9"(W) x 3.4"(H) X 6.3"(L)
Some of the PSUs that will fit:
Corsair TX750W Dimension: 5.9(W) x 3.4(H) X 6.3(L);
Seasonic M12-600 M12-700 150*160*86 mm (5.9x6.3x3.4)
OCZ GameXStream 850W 150 x 140 x 86mm
OCZ GameXStream 1010W 150 x 140 x 86mm
The following doesn't take standard atx power supply, but both athena and in-win take the next best micro atx with a maximum wattage of 550W which is much better than what most mini cases offer. View the following link, then the in win link:
The answer to your question in your original post is yes, a 600 watt power supply will fit in the Lian Li PC-AO5.
I am a bit confused about what you really want because the title of your thread is "need a small atx case that will fit a 600 watt psu..." That Lian Li case is a mid-tower atx case and it's not exactly small. There is a category of smaller micro-atx cases available and some of them can take a 750 watt psu, a standard size atx motherboard, longer video cards, mutiple 120mm case fans, and 90mm tower style cpu heatsinks.
It would really help if you posted a list of your pc components.