Issue about 802.11n speed of OmniTIK U-5HnD

Hi there

this my first post on here. i just bought a OmniTIK U-5HnD last month and now is working fine but in low speed.
before my question, here is my network:

NAS (1000Mbps) -- Switch A (1000Mbps) -- Switch B (1000Mbps)  -- U-5HnD (5Ghz-onlyN) -- laptop(802.11N)

The fact is wireless speed is around 40Mbps while copying 2GB file from NAS via U-5HnD. If i plug a cat.6 cable in Switch B and set laptop wireless OFF, then the speed is around 120MB/s (about 1000Mbps).

i had checked U-5HnD spec. file and it say 199Mbps max. Therefore, what can i do to reach max speed?

Here is wireless config::

[admin@SnS-ROS] /interface wireless print
Flags: X - disabled, R - running 
 0  R name="wlan1" mtu=1500 mac-address=00:0C:42:DA:32:E9 arp=enabled interface-type=Atheros 11N mode=ap-bridge ssid="SnS-5GHz" frequency=5220 band=5ghz-onlyn channel-width=20mhz 
      scan-list=default wireless-protocol=any wds-mode=disabled wds-default-bridge=none wds-ignore-ssid=no bridge-mode=enabled default-authentication=yes default-forwarding=yes 
      default-ap-tx-limit=0 default-client-tx-limit=0 hide-ssid=no security-profile=ouzy compression=no

Another question is:

NAS (1000Mbps) -- Switch A (1000Mbps) -- Switch B (1000Mbps)  -- U-5HnD (DHCP, DNS, SSID:B, 192.168.88.x) -- laptop A(802.11N)
                            |
                        AP-A(DNS, DHCP, PPPoE, SSID:A, 802.11abg, 192.168.1.x) -- laptop B
                            |
                         Cable modem

if i wanna AP-A as the only DNS,DHCP server and U-5HnD ip would like 192.168.1.4. IS it possible? and how-to config U-5HnD?
if i set AP-A and U-5HnD use SAME SSID, is it possible?