This evening I found my self reading the AR7200BX manual and came across some info that I thought you would find valuable so here are some quotes from the manual:
The AR7200BX is perfect for mini (up to 450 class) helicopters. Using an optional DSMX remote receiver adds necessary path diversity for even the largest electric, glow, gas and turbine-powered helicopters.The AR7200BX is compatible with all Spektrum and JR® aircraft radios that support DSM2™ and DSMX technology.
Important: When using the AR7200BX with larger helicopters (500-size and larger): It is necessary that you connect a DSMX remote receiver (not included) to the AR7200BX before binding.
The DSMX remote receiver is often called a "satellite receiver" and reason for wanting one on a bigger heli is to improve signal diversity by introducing more antennas to prevent a black out due to a bigger heli having more "blind spots" so-to-speak.
There's a DX6i package that comes with a satellite receiver and rechargeable batteries. It costs bout $209. But that's a better price than buying these items separately.
Type: DSM receiver and BeastX flybarless technology
Channels: 7 (8 channels are available, however, Channel 5 is only used as an internal gain channel for the tail gyro).
Modulation: DSM2, DSMX
Main Receiver Dimensions: 36mm x 28mm x 13 mm/1.42 in x 1.1 in x .51 in (Length x Width x Height)
Main Receiver Weight: 0.66 oz (18.6 g)
Voltage Range: 3.5 to 8.5V
Frame Rate: 11ms
Compatibility: All DSM2 and DSMX aircraft transmitters and module systems
So why is Resolution and Frame Rate important? Because you'd want a transmitter that matches well with the AR7200BX. Although my DX6i is working just fine with the AR7200BX, I currently do not know what the DX6i specs are for frame rate and resolution. The DX7s is speced at 11ms and 22ms frame rates and up to 2048 resolution.
The explanation of resolution gets more interesting...
Source (see post #2): http://www.rcgroups.com/forums/showthread.php?t=1704299
A transmitter tells the receiver where to instruct the servos to go. On a 1024 system, there are 1024 positions available. The receiver converts that number for each channel into a proportional pulse for each servo.
The '1024' number has to accommodate full stick movement, full trims and full throws. You only use all 1024 positions when everything is at an extreme. In other words, you normally use much less than 1024 steps on a 1024 radio.
The amount of servo rotation for each change in position is constant; ie each step is a fixed size. However, the amount of rotation on a 1024 radio will be double that of a 2048 radio. In other words, both may move the servo through 180 degrees but the 2048 system has finer control.
One Tx trim click is about 4 of 1024 steps but this can be adjusted on more expensive radios.
The DX7 and DX8 can have 150% travel each way. This setting gives you the potential for 1024 steps. At the default 100% settings you only get 2/3 throw (100 out of 150% max) from say position 170 to 853 with 511 the center position. So in normal use at default settings you only use about 683 steps of servo resolution with a 1024 radio.
The DX6i only has 125% Travel Adjust each way. So the servos can be made to move between positions 85 to 938. The DX6i cannot make the receiver generate pulses corresponding to positions 0-84 and 939-1023.
The numbers I've used may not be exact but hopefully help explain how the settings work and interract.
I swear on the 4F200 with the Futaba S3154 cyclic servos, after I installed the AR7200BX, I was able to get more travel on the servos. This is comparing to when the Walkera 2601 TX was used with the S3154 servos. So I am guessing the DX6i has higher resolution than the 2601?
Still learning... I am.