"is further underscored" is correct and usable in written English.
You can use it when you want to emphasize something or strengthen an existing point. For example, "The importance of this issue is further underscored by the number of experts who have weighed in on the matter."
The show's fluidity is further underscored by the sheer speed of its performance.
The progression is further underscored by the differing dance styles of the three acts.
"That point is further underscored by the decision in 1900 to open a separate Workingmen's Library for the city's laboring classes.
The substantive economic irrelevance of today's proceedings is further underscored by the fact that the government's public expenditure plans, which under Margaret Thatcher's chancellors became the raison d'être of the autumn statement, have all been signed and sealed long ago.
The intractability of the country's problems is further underscored by "Children of Haiti," an "Independent Lens" documentary by Alexandria Hammond that is also showing on Tuesday night on PBS.
Moreover, for those designers who design their own video processing algorithms using general-purpose DSP to circumvent the cost and limitations imposed by these suites of standard solutions, the need for a simple analogue video interface is further underscored.
That finally has begun to change — although, again, the sectarian hue of the regime, and of the rebel opposition, is being further underscored by the defections.
The potential for online video was further underscored on Wednesday when, at the Condé Nast Entertainment presentation during the NewFronts, executives announced additions to their digital video network.
Later in the day, the swift pace of change in the post-Bush political landscape in Texas was further underscored when Senator Phil Gramm, a conservative Republican, said he would not seek re-election next year.
