ZIX-2.0 format
Here is the break down of a simple ZIX-2.0 archive. 
 offset                    h e x    d a t a                       ascii data
00000000  File Magic: WINZIX57 49 4e 5a 49 58 Unknown constant: 0x000300 03  Unknown constant: 0x000100 01 Compressed size: 39 bytes00 00 00 00 00 00  |WINZIX..........|
00000010  Compressed size: 39 bytes00 27 Uncompressed size: 33 bytes00 00 00 00 00 00  00 21 Filename length: 12 characters00 00 00 00 00 00  |.'.......!......|
00000020  Filename length: 12 characters00 0c Unknown constant: 0x0000 MD5 hash15 17 b1 01 4e  63 3e 40 4d da 59 11 ab  |.....±.Nc>@MÚY.«|
00000030  MD5 hashe8 c3 67 Filename: one-file.txt6f 6e 65 2d 66  69 6c 65 2e 74 78 74 Compressed file data78  |èÃgone-file.txtx|
00000040  Compressed file data9c 2b c9 c8 2c 56 00 a2  82 fc 62 85 c4 a2 e4 8c  |.+ÉÈ,V.¢.üb.Ä¢ä.|
00000050  Compressed file datacc b2 54 85 8c c4 62 85  fc bc 54 85 b4 cc 9c 54  |̲T..Äb.ü¼T.´Ì.T|
00000060  Compressed file data2e 00 cd 53 0b b1                                 |..ÍS.±|
Notes:
Every ZIX archive has a global header which looks like:

offset size meaning value
0 6 bytes File Magic WINZIX
6 2 bytes Unknown (format version?) 0x0003


Every file in the ZIX archive has a file header which looks like:

offset size meaning value
8 2 bytes Unknown 0x0001
10 8 bytes compressed size (in bytes) 0x0000000000000027 (39)
18 8 bytes uncompressed size (in bytes) 0x0000000000000021 (33)
26 8 bytes filename length (in characters) 0x000000000000000c (12)
34 1 byte Unknown 0x00
35 16 bytes MD5 hash (of uncompressed file) 1517b1014e633e404dda5911abe8c367
51 see {filename length} filename (with possible directory names) one-file.txt
?? see {compressed size} compressed file data {arbitrary data}
Additional file records are simply repeated right ater the previous one.