possible to you add an external RF PA LNA to a chip that has internal PA LNA?
It should be possible to increase the sensitivity of your system by putting a lower noise LNA in between an external antenna and the chip's internal LNA.  

The noise figure and thus sensitivity of your system will be dominated by the noise of the first amplifier in the receive chain, see the pages on noise figure and cascade analysis by Microwaves101.  Your total system noise figure \$F\$ will be:

$$
F=F_1 + \frac{F_2-1}{G_1}
$$

where \$F_1\$ and \$G_1\$ is the noise figure and gain of the first LNA and \$F_2\$ is the noise figure of the second LNA.  In your case, \$F_2\$ is the noise figure of the internal LNA.

Your new chip's minimum receive power, ie. sensitivity, of -94dBm is related to noise figure by 

$$
S_{min} = SNR_{min} k T_O B F
$$

where \$SNR_{min}\$ is the minimum signal-to-noise ratio of the receiver, \$k\$ is the Boltzmann constant, \$T_O\$ is the system temperature, \$B\$ is the system bandwidth, and \$F\$ is the receiver noise figure.  While you can't change the chip's \$SNR_{min}\$ you can possibly decrease the noise figure by using a lower noise external LNA.  Without more information it's hard to say what is the noise figure of the internal LNA so as to predict what the noise figure of the external LNA needs to be.

As a side note, I wouldn't neglect examining the filtering and impedance matching between the external antenna and chip, both can greatly influence the overall receiver sensitivity.