6300 No preselector?

This from Steve N5AC from an earlier post:
Superhet receivers have limited dynamic range and are forced to use filtering techniques at the front end and each stage to prevent overload.  The FLEX-6300 is a direct sampling receiver and by nature will consume the entire HF spectrum at once.  The overload point is simply the max voltage input to the A-to-D Converter (ADC) which is +7dBm (5mW) for the FLEX-6300.  This is a very large signal in the front end of the receiver and it is rare that you would encounter this level of signal. 

You could see a signal like this when there are other strong transmitters co-located with the FLEX-6300.  This is design difference in the FLEX-6500 and FLEX-6700 -- they both have preselectors. You have to decide for your environment if they will be necessary.  If you are going to run a multi-multi contest station, you will almost certainly want the preselectors.  If you are running the FLEX-6300 from your shack and do not have a next door neighbor that is a ham and runs power, you are much less likely to need preselectors.  At my house, I would never need them.

There is a broadcast filter in the FLEX-6300 which is the most likely place to find large signals so these signals will be knocked down considerably unless you are listening in that portion of the band.  If you need a more definitive answer, you can take readings at your operating point -- connect a power meter that is band limited to 1.8-54MHz and see what the total power reading on the meter is or alternately use a spectrum analyzer.  For reference, a +7dBm signal is S9+80dB!

Pavel, i think base on this picture:

and a bit knowledge of the SSDR, you can utilize an external preselector what are compatible with external RX/TX signal where for RX you can use XVTR circuit and for TX ANT1 as default, or you can use 100watts compatible preselector (BPF) driving via DDutil 

You know everything are depends, you are in Software Defined radio community :-) It is up to you